# Top 10 Chrome PDF Extensions: The Great Comparison > Compare the 10 best PDF extensions for Chrome. We tested Web Highlights, Smallpdf, Adobe Acrobat, Kami and more on reading, editing and signing. - Author: Marius Bongarts - Published: 2026-08-28 - Updated: 2026-08-28 - Tags: Chrome Extension, comparison, Tools - Reading time: 23 min - URL: https://web-highlights.com/blog/best-pdf-chrome-extensions/ --- A PDF arrives, you open it in Chrome, and that’s about where the browser stops helping. Chrome’s own viewer has picked up a pen and a highlighter over the years, but whatever you mark stays inside that one file on that one machine. Two weeks later you know you read the thing. You just can’t find the sentence. That gap is why the extension stores are full of PDF tools. Some are editing suites from names you’d recognise — convert, compress, merge, sign. Others are highlighters built for people who read papers all day and want the marked passages back afterwards. A few try to be both, and the quality swings hard: polished and genuinely free at one end, basics behind a paywall at the other. I wanted to know which ones hold up. In this article I compare the 10 best PDF extensions on the Chrome Web Store, ranked by score. Several are also on Edge and Firefox, but every number below is the Chrome listing unless I say otherwise. One disclosure before the list: Web Highlights is mine, and it ranks first here. The scores come from  [Tooltivity](https://tooltivity.com) 's own review methodology, not from me — and I’ll say plainly what each of the other nine does better. ### List of the Best PDF Extensions for Chrome: - [PDF & Web Highlighter + AI Summary & Notes](https://tooltivity.com/extensions/web-highlights) - [Glasp Web Highlighter](https://tooltivity.com/extensions/glasp-web-highlighter) - [Smallpdf — Edit, Convert, Compress, & AI Summarize PDF](https://tooltivity.com/extensions/smallpdf) - [Adobe Acrobat: PDF edit, convert, sign tools](https://tooltivity.com/extensions/adobe-acrobat) - [Kami for Google Chrome](https://tooltivity.com/extensions/kami) - [Hypothesis - Web & PDF Annotation](https://tooltivity.com/extensions/hypothesis) - [DocHub - Sign PDF from Gmail](https://tooltivity.com/extensions/dochub) - [Xodo | PDF Editor, Converter & Merger](https://tooltivity.com/extensions/xodo) - [Diigo Web Collector - Capture and Annotate](https://tooltivity.com/extensions/diigo-web-collector) - [Weava Highlighter: PDF & Web](https://tooltivity.com/extensions/weava) If you’d rather see everything side by side first, here’s the  [comparison table of all Chrome PDF extensions](https://tooltivity.com/extensions/compare/category/pdf-tools/chrome) , with ratings, pricing, and features in one grid: ![Comparison table of all Chrome PDF extensions with ratings](https://web-highlights.com/blog/content/images/2026/08/screenshot-pdf-tools-comparison-extensions.webp) *Comparison of all Chrome PDF Extensions* ## [1\. PDF & Web Highlighter + AI Summary & Notes](https://tooltivity.com/extensions/web-highlights) ![PDF and Web Highlighter showing highlights and notes in the sidebar](https://tooltivity.com/data/tooltivity/apps/web-highlights/images/gallery-image-1.webp) Web Highlights opens the list with the strongest numbers on it: 200,000 downloads on the Chrome Web Store and a 4.83/5 rating from 4,946 reviews, with the most recent 100 sitting at 4.79. Flat, in other words — which several tools further down this list cannot say. It’s also on Edge (4.6/5 from 101 reviews across 18,069 downloads) and Firefox (4.84/5 from 49 reviews, 1,840 downloads). The reason a highlighter belongs in a PDF roundup is what happens after you highlight. Open a PDF — a link, a local file, or one you upload into your library up to 30 MB — mark what matters, add notes, and it all lands in a searchable library instead of in one copy of one file. Download that PDF again and every highlight comes back embedded as a real annotation: its own colour, your notes as comments, the text still selectable, and Acrobat, Preview, and Edge all read them as their own. Highlights that were already in a file import the other direction with one click. There’s a step-by-step version in our guide to  [annotating a PDF in Chrome](https://web-highlights.com/blog/annotate-a-pdf-in-chrome/) . Two things sit on top of that. The AI — summaries, chat, flashcard drafting — runs on your own device through the browser’s built-in model, so a contract or an unpublished draft doesn’t get uploaded anywhere to be summarised. And any highlight can become a Q/A flashcard, scheduled by the SuperMemo spaced-repetition algorithm. That sounds like a strange thing to put in a PDF tool right up until the third time you actually remember what a paper argued. You don’t need an account to start. Install it, select text, and the highlight is saved and restored the next time you open the page. If you’d rather not install anything at all, our  [free online PDF highlighter](https://web-highlights.com/blog/free-online-pdf-highlighter-highlight-any-pdf-no-install/)  runs the same read-highlight-download loop in a plain browser tab. ### Key Features - **Website Highlighting**  – Highlight text on any website, restored automatically on your next visit - **PDF Highlighting**  – Mark up online, local, and uploaded PDFs (up to 30 MB) in the built-in viewer - **Real PDF Annotations**  – Download a PDF with your highlights embedded as standards-compliant annotations that Acrobat and Preview can edit - **Annotation Import**  – Highlights already in a file, from Acrobat or Preview, come back in with one click - **AI Summary**  – Summarise a page, a PDF, or your own highlights on your device - **AI Chat**  – The on-device model reads the whole page, so you can ask questions about a website, PDF, or YouTube video - **Multiple Colors**  – Use different colors to separate arguments, quotes, and to-dos - **Note-Taking**  – Add a note to a highlight, or write a page note about the whole document with full formatting - **Reader Mode**  – Read a PDF as clean text, with headings, lists, and two-column papers handled properly - **Tagging**  – Organize highlights and notes with tags across the whole library - **Collections (Folders)**  – Keep documents in a nested folder tree with drag & drop, alongside tags - **Cross-Device Sync**  – Sync your library between browsers and machines via the cloud - **Export Options**  – One-click export to Notion and Capacities on the Ultimate plan, plus copy as Markdown for Obsidian, or export to an HTML or PDF file - **Reminders**  – Snooze a document and get an email when it’s time to read it - **Flashcards & Spaced Repetition**  – Turn a highlight into a Q/A card and review it with the SuperMemo algorithm, with the AI drafting whole decks on your device ### Pros & Cons **Pros:** - Excellent free version - No account required to start - Highlights download as real, editable PDF annotations - AI summaries and chat run on your own device - Spaced-repetition flashcards from your highlights - Collections, tags & notes - Chrome, Edge and Firefox, with a web app to match **Cons:** - Cloud sync is free for 7 days, then part of a paid plan - No native mobile app yet — the web app installs as a PWA - No shared team workspace; you share single pages by public link - The on-device AI wants a one-time model download and a lot of free disk space as headroom - Not a PDF editor — no converting, compressing, page reordering, or e-signing ### Who is this great for? Web Highlights is built for people who read PDFs in order to use them later: students working through a reading list, researchers pulling quotes out of journal articles, anyone whose job involves finding the one clause that matters in a forty-page document. The library, the tags, and the search are the point — the highlighting is just how things get in there. It’s a poor fit if your PDF problems are administrative. Filling a tax form, compressing a scan under an email limit, signing a lease, converting a deck to Word — none of that is here, and four tools further down this list do it better. Pick Web Highlights for reading and research; pair it with one of them for the paperwork. ### Compared to others Among the highlighters,  [Glasp](https://tooltivity.com/extensions/glasp-web-highlighter)  has the bigger community and lets you pick between ChatGPT, Claude, and Gemini, where our AI is whatever your browser ships; the trade is that Glasp’s free tier publishes your highlights by default.  [Hypothesis](https://tooltivity.com/extensions/hypothesis)  beats us outright on group reading — threaded replies on a shared document are something we simply don’t do. Against  [Weava](https://tooltivity.com/extensions/weava)  and  [Diigo](https://tooltivity.com/extensions/diigo-web-collector) , both older research collectors, the gap is upkeep more than ambition. And next to  [Adobe Acrobat](https://tooltivity.com/extensions/adobe-acrobat)  or  [Smallpdf](https://tooltivity.com/extensions/smallpdf) , we’re not in the same category at all: they edit documents, we read them. ### Detailed comparisons [PDF & Web Highlighter vs Glasp](https://tooltivity.com/extensions/compare/web-highlights-vs-glasp-web-highlighter)  •  [PDF & Web Highlighter vs Weava](https://tooltivity.com/extensions/compare/web-highlights-vs-weava)  •  [PDF & Web Highlighter vs Hypothesis](https://tooltivity.com/extensions/compare/web-highlights-vs-hypothesis) ### Rating Summary Web Highlights has 200,000 downloads on Chrome with a 4.83/5 average from 4,946 reviews, holding 4.79 across the most recent 100.  [Tooltivity](https://tooltivity.com)  gave PDF & Web Highlighter a score of  **9.78/10** .  [Check out the full review here](https://tooltivity.com/extensions/web-highlights) . > [**Install Web Highlights on your browser**](https://web-highlights.com/install) — Install our browser extension to highlight & annotate Websites & PDFs – free, easy to use, no sign-up required. --- ## [2\. Glasp Web Highlighter](https://tooltivity.com/extensions/glasp-web-highlighter) ![Glasp Web Highlighter sidebar with saved highlights](https://tooltivity.com/data/tooltivity/apps/glasp-web-highlighter/images/gallery-image-1.webp) Glasp treats your notes as something to share rather than something to keep. It has 500,000 downloads on the Chrome Web Store and a 4.46/5 rating from 978 reviews, though the recent trend has softened: the last 100 reviews average 4.22, a step below the long-run number. What you get is a social layer on top of web, PDF, and YouTube highlighting. Summarise what you saved with ChatGPT, Claude, or Gemini, push it to Obsidian, Notion, or Roam, pull in your Kindle highlights, and browse what other readers have marked on the same article. It’s a real second-brain system, and the model choice alone is something no other tool here offers. The catch is the default: on the free plan your highlights are public, and private notes are a paid feature. Worth knowing before you highlight a work document. ### Key Features - **Multi-Platform Highlighting**  – Highlight websites, PDFs, and YouTube videos in several colors - **AI-Powered Summaries**  – Generate summaries with ChatGPT, Claude, or Gemini - **Social Learning Network**  – See what other readers highlighted and follow people whose reading you like - **Cross-Platform Sync**  – Your highlights follow you across devices automatically - **Export Integration**  – Send highlights to Obsidian, Notion, Roam Research, and other note apps - **Kindle Integration**  – Import and sync the highlights from your Kindle books ### Pros & Cons **Pros:** - Broad feature set for the price - Large, genuinely active community - Choice of three AI models - Flexible exports to note apps - Kindle highlights come along **Cons:** - Free tier makes your highlights public - Premium plans are steep for casual use - Recent reviews are drifting down - Occasional technical hiccups ### Who is this great for? Glasp suits people who learn in the open — creators, curators, students who like seeing which passages everyone else stopped at. If discovery is part of how you read, nothing else in this comparison gives you that. It’s also the pick if you already have a note system you love. The exports to Obsidian, Notion, and Roam are the most flexible here, and the Kindle import closes a gap most highlighters ignore. Just switch your default to private early if your reading isn’t meant for an audience. ### Compared to others Glasp and  [PDF & Web Highlighter](https://tooltivity.com/extensions/web-highlights)  pull in opposite directions: Glasp is social, cloud-AI, account-first, while we’re private, on-device, and usable without signing up. Against  [Weava](https://tooltivity.com/extensions/weava) , Glasp wins on features, community, and maintenance, though both want an account before you highlight anything. And where  [Diigo](https://tooltivity.com/extensions/diigo-web-collector)  is a research collector from an earlier internet, Glasp is the modern answer to the same idea. ### Detailed comparisons [Glasp vs PDF & Web Highlighter](https://tooltivity.com/extensions/compare/glasp-web-highlighter-vs-web-highlights)  •  [Glasp vs Weava](https://tooltivity.com/extensions/compare/glasp-web-highlighter-vs-weava)  •  [Glasp vs Diigo](https://tooltivity.com/extensions/compare/glasp-web-highlighter-vs-diigo-web-collector) ### Rating Summary Glasp has 500,000 downloads on Chrome with a 4.46/5 rating from 978 reviews, easing to 4.22 across the last 100.  [Tooltivity](https://tooltivity.com)  gave Glasp a score of  **8.88/10** .  [Check out the full review here](https://tooltivity.com/extensions/glasp-web-highlighter) . --- ## [3\. Smallpdf — Edit, Convert, Compress, & AI Summarize PDF](https://tooltivity.com/extensions/smallpdf) ![Smallpdf toolbar popup listing PDF tools](https://tooltivity.com/data/tooltivity/apps/smallpdf/images/gallery-image-1.webp) If the first two entries are about reading, Smallpdf is about doing. It packs a desktop-grade PDF suite into one toolbar button, and the store agrees: 2 million downloads and a 4.64/5 rating from 2,998 reviews, with the last 100 at 4.36 — cooler than the all-time average, but still the second-highest recent score in this comparison. Breadth is the whole pitch. Roughly twenty tools sit behind that button: compress, convert to and from Word, Excel, PowerPoint and JPG, merge, split, rotate, e-sign, and an AI assistant that summarises or answers questions about a document. The basics are free and often don’t even need an account. Compression is the one people mention most — a bloated scan comes back a fraction of its size without any visible damage. The heavier editing hands you over to the Smallpdf website and, before long, to a Pro subscription. ### Key Features - **PDF Compression**  – Shrink oversized files enough to clear an email attachment limit - **Convert To and From PDF**  – Word, Excel, PowerPoint and JPG in both directions - **Merge & Split**  – Combine a pile of files or pull one document apart, no account needed for the basics - **Edit PDFs**  – Drop text, images, shapes, and annotations onto a page - **E-Sign Documents**  – Draw or type a signature and place it on a contract - **Organize Pages**  – Rotate, reorder, and delete pages to tidy up a scan - **AI PDF Assistant**  – Summarise a long document or ask it questions instead of reading end to end - **One-Click Access**  – Every tool in a single popup, nothing to install ### Pros & Cons **Pros:** - Huge all-in-one toolkit - Compression that actually works - Free and account-free for the basics - Almost no learning curve - Handy e-signing and AI summaries **Cons:** - Real editing sits behind Pro - Free tier has tightened over time - Recurring billing and cancellation complaints - Editing bounces you out to the website ### Who is this great for? Smallpdf is for the person whose PDF work is a rotating list of chores: compress a scan today, convert a deck tomorrow, sign a contract next week. It rewards range rather than depth, and it’s fast enough that you stop thinking about it. It’s especially good for occasional users who mostly need free compression and conversion and don’t want desktop software. If PDFs become a daily job, watch where the free line now sits, and set a calendar reminder before any Pro trial renews — that’s what most of the angry reviews are about. ### Compared to others Smallpdf sits between the heavyweights and the light tools. It undercuts  [Adobe Acrobat](https://tooltivity.com/extensions/adobe-acrobat)  on price and folds more into its free allowance, though Acrobat goes deeper where documents have to hold up professionally. Against  [Xodo](https://tooltivity.com/extensions/xodo) , Smallpdf is the more polished and more reliable of the two. For signing alone,  [DocHub](https://tooltivity.com/extensions/dochub)  covers the whole loop without a subscription. And for reading and annotating rather than processing,  [PDF & Web Highlighter](https://tooltivity.com/extensions/web-highlights)  keeps your notes in a library instead of handing you a modified file. ### Detailed comparisons [Smallpdf vs Adobe Acrobat](https://tooltivity.com/extensions/compare/smallpdf-vs-adobe-acrobat)  •  [Smallpdf vs Xodo](https://tooltivity.com/extensions/compare/smallpdf-vs-xodo)  •  [Smallpdf vs DocHub](https://tooltivity.com/extensions/compare/smallpdf-vs-dochub) ### Rating Summary Smallpdf has 2,000,000 downloads on Chrome with a 4.64/5 rating from 2,998 reviews, holding 4.36 over the last 100.  [Tooltivity](https://tooltivity.com)  gave Smallpdf a score of  **8.73/10** .  [Check out the full review here](https://tooltivity.com/extensions/smallpdf) . --- ## [4\. Adobe Acrobat: PDF edit, convert, sign tools](https://tooltivity.com/extensions/adobe-acrobat) ![Adobe Acrobat extension opening a PDF in Adobe’s viewer inside Chrome](https://tooltivity.com/data/tooltivity/apps/adobe-acrobat/images/gallery-image-1.webp) Adobe invented the format, and the install count reflects it: 307 million downloads on the Chrome Web Store with a 4.40/5 rating from 62,815 reviews. Recent sentiment runs a little below that at 4.18 across the last 100 — not a collapse, and worth reading in context: the recurring complaints are about pricing and upgrade prompts rather than how Acrobat handles a PDF. Install it and Chrome hands PDFs to Adobe’s own viewer, where reading, form-filling, commenting, and signing are free. Converting, compressing, combining, and editing actual text belong to an Acrobat Pro subscription. As a free reader and signer it’s dependable in a way nothing else here quite matches; as a full editor it wants your card. If the subscription is the part you’re stuck on, we keep a roundup of  [the best Adobe PDF alternatives](https://web-highlights.com/blog/best-adobe-pdf-alternatives/)  that covers what you give up by leaving. ### Key Features - **View & Read PDFs**  – Open any PDF in Adobe’s viewer inside Chrome - **Fill & Sign**  – Complete forms and add a recognised e-signature, free - **Comment & Annotate**  – Sticky notes, highlights, and text markup for review rounds - **Convert To & From PDF**  – Web pages, images, and Office files in and out (Pro) - **Compress & Reduce**  – Get bulky files under attachment limits (Pro) - **Combine & Organize**  – Merge files, then reorder, insert, or delete pages (Pro) - **Edit Text & Images**  – Change wording and swap images in the document itself (Pro) - **AI Assistant**  – Ask questions about a document and generate summaries (paid add-on) ### Pros & Cons **Pros:** - The most complete PDF toolkit there is - Free viewing, filling, signing, commenting - Signatures nobody will question - Handles files other viewers choke on - Runs inside Chrome, no desktop install **Cons:** - Real editing locked behind Pro - Pro subscription is expensive - Constant upgrade prompts - The AI assistant is pushy - Can slow Chrome down noticeably ### Who is this great for? Acrobat is the safe default when the document matters — legal, admin, finance, anything where a signature has to be trusted and the layout has to survive whoever opens it next. If PDFs are the medium of your job rather than a nuisance in it, Pro pays for itself. It also works fine for light users who stay inside the free basics and are willing to dismiss the upgrade prompts. What it isn’t is a good deal for someone who edits one line of text a month. That’s the case where the recent reviews get sharp, and it’s a fair complaint. ### Compared to others Nothing here matches Acrobat for depth, and nothing here charges like it either.  [Smallpdf](https://tooltivity.com/extensions/smallpdf)  and  [Xodo](https://tooltivity.com/extensions/xodo)  fold editing, conversion, and compression into more generous free tiers, so lighter users usually get further without paying. For signing specifically,  [DocHub](https://tooltivity.com/extensions/dochub)  closes the loop from Gmail with no subscription at all. Acrobat wins on trust and completeness; everything else wins on cost and immediacy. ### Detailed comparisons [Adobe Acrobat vs Smallpdf](https://tooltivity.com/extensions/compare/adobe-acrobat-vs-smallpdf)  •  [Adobe Acrobat vs Xodo](https://tooltivity.com/extensions/compare/adobe-acrobat-vs-xodo)  •  [Adobe Acrobat vs DocHub](https://tooltivity.com/extensions/compare/adobe-acrobat-vs-dochub) ### Rating Summary Adobe Acrobat has 307,000,000 downloads on Chrome with a 4.40/5 rating from 62,815 reviews, and 4.18 across the last 100.  [Tooltivity](https://tooltivity.com)  gave Adobe Acrobat a score of  **8.50/10** .  [Check out the full review here](https://tooltivity.com/extensions/adobe-acrobat) . --- ## [5\. Kami for Google Chrome](https://tooltivity.com/extensions/kami) ![Kami annotation tools open on a worksheet PDF](https://tooltivity.com/data/tooltivity/apps/kami/images/gallery-image-1.webp) Kami is close to synonymous with PDF annotation in schools, and the reach shows: 6 million downloads and a 4.56/5 rating from 8,401 reviews. Then look at the recent window. The last 100 reviews average 3.87, and that gap between the all-time score and the current one is the largest of any tool in the top half of this list. It isn’t noise — it lines up with a paywall push that moved features longtime users had for free. What it does, it does thoroughly. Any document becomes a shared workspace: highlight, draw, and drop text, voice, or video comments onto a PDF, split and merge files, run OCR on a scanned worksheet, and annotate together in real time through Google Classroom. For teacher feedback specifically, the voice and video comments are something no other tool in this comparison offers, and they’re the reason schools stayed. ### Key Features - **PDF Annotation**  – Highlight, underline, strike through, and draw freehand, then save the markup back into the file - **Voice & Video Comments**  – Leave feedback as audio or a short clip instead of typing it - **Real-Time Collaboration**  – Several people annotate the same document at once - **Split & Merge PDFs**  – Break up or combine documents without leaving the browser - **OCR Text Recognition**  – Turn scanned worksheets into selectable, searchable text - **Google & Microsoft Integration**  – Classroom, Drive, and OneDrive with auto-save - **Drawing & Handwriting Tools**  – Pen, shapes, and equation tools tuned for maths and touchscreens - **Reading Support**  – Dictionary and read-aloud helpers aimed at classroom accessibility ### Pros & Cons **Pros:** - Deepest PDF markup toolkit here - Voice and video feedback - Real-time classroom collaboration - Google Classroom integration that works - Split, merge, and OCR built in **Cons:** - Key features moved behind a paywall - Sign-in required before anything happens - Highlighting can be unreliable - Support is slow to respond - Recent ratings have fallen hard, from 4.56 all-time to 3.87 ### Who is this great for? Kami is for teachers, and it’s at its best in a classroom already running on Google Classroom and Drive. Marking up worksheets together and leaving rich feedback is a job it does better than anything else in this comparison. Individuals who just want to annotate the occasional PDF will feel every bit of friction it was designed to carry — the sign-in, the institutional onboarding, the upgrade nudges. And given where the recent reviews sit, it’s worth checking what your school’s plan actually covers before building a term around it. ### Compared to others [Hypothesis](https://tooltivity.com/extensions/hypothesis)  is the other education favourite, but they split by purpose: Hypothesis is built for scholarly discussion on the open web and costs nothing, while Kami is a heavier markup suite for handouts and homework. For solo annotation,  [PDF & Web Highlighter](https://tooltivity.com/extensions/web-highlights)  is lighter and needs no account, but has no live collaboration and no voice comments. And for editing a document rather than marking it up,  [Adobe Acrobat](https://tooltivity.com/extensions/adobe-acrobat)  goes further than Kami tries to. If you’re weighing methods rather than brands, our guide on  [how to annotate a PDF](https://web-highlights.com/blog/how-to-annotate-a-pdf/)  walks through the options. ### Detailed comparisons [Kami vs Hypothesis](https://tooltivity.com/extensions/compare/kami-vs-hypothesis)  •  [Kami vs PDF & Web Highlighter](https://tooltivity.com/extensions/compare/kami-vs-web-highlights)  •  [Kami vs Adobe Acrobat](https://tooltivity.com/extensions/compare/kami-vs-adobe-acrobat) ### Rating Summary Kami has 6,000,000 downloads on Chrome and a 4.56/5 all-time rating from 8,401 reviews, though recent sentiment has dropped sharply to 3.87 across the last 100.  [Tooltivity](https://tooltivity.com)  gave Kami a score of  **8.23/10** .  [Check out the full review here](https://tooltivity.com/extensions/kami) . --- ## [6\. Hypothesis - Web & PDF Annotation](https://tooltivity.com/extensions/hypothesis) ![Hypothesis annotation sidebar with a threaded reply on a document](https://tooltivity.com/data/tooltivity/apps/hypothesis/images/gallery-image-1.webp) Hypothesis is the quiet outlier: free, open source, run by a nonprofit, with no paid tier waiting behind a button. It has 200,000 downloads and a 4.12/5 rating from 223 reviews, and the number barely moves — 4.05 across the last 100, which in this comparison counts as remarkable stability. What it does is lay a shared annotation layer over the web. Highlight and annotate pages, PDFs, and EPUBs, keep the notes private, publish them, or put them in a group; reply to anyone else’s note and hold the whole discussion on top of the text. That’s the part we can’t match, and it’s why the tool is so entrenched in universities. If you’re a student choosing between the two, I wrote a longer  [Web Highlights vs Hypothesis comparison](https://web-highlights.com/blog/web-highlights-vs-hypothesis-for-students/)  that goes through it properly. ### Key Features - **Web & PDF Annotation**  – Highlight web pages, PDFs, and EPUBs from one extension - **Private, Public & Group Notes**  – Choose per annotation who gets to see it - **Collaborative Groups**  – Spin up a group for a class or research team and read the same document together - **Threaded Replies**  – Discuss a passage in a thread anchored to that passage - **Tags & Full-Text Search**  – Tag notes and search your whole annotation history - **Hide/Show Toggle**  – Clear every highlight off the page for a clean read, then bring them back - **Persistent PDF Notes**  – Annotations stay attached to a PDF, so the same file is recognised later - **Open API**  – Pull your annotations into Obsidian, Readwise, or Logseq ### Pros & Cons **Pros:** - Free, open source, nonprofit - Best group annotation in this comparison - Private, public, or group notes per annotation - Steady ratings, no paywall creep - Open API and real integrations **Cons:** - Account required before you highlight anything - Frequent logouts and dropped sessions - Only one highlight color - Interface shows its age - Public-by-default trips people up ### Who is this great for? Hypothesis is for people who read together — seminar groups, research teams, classes working through the same paper. If the point of annotating is that someone else will answer, this is the tool, and it costs nothing. It also appeals to anyone who wants open-source software backed by an organisation with no reason to monetise their reading. Set your default to private on day one, and make peace with a single highlight colour. ### Compared to others Against  [Kami](https://tooltivity.com/extensions/kami) , Hypothesis is free and open where Kami is institutional and paid, but Kami’s PDF markup is far richer. Compared to  [PDF & Web Highlighter](https://tooltivity.com/extensions/web-highlights) , it trades our colors, on-device AI, and no-account start for something we don’t have at all: a conversation on the page. And like  [Glasp](https://tooltivity.com/extensions/glasp-web-highlighter) , it puts a shared layer at the centre — the difference being that Hypothesis is nonprofit rather than community-and-AI driven. ### Detailed comparisons [Hypothesis vs Kami](https://tooltivity.com/extensions/compare/hypothesis-vs-kami)  •  [Hypothesis vs PDF & Web Highlighter](https://tooltivity.com/extensions/compare/hypothesis-vs-web-highlights)  •  [Hypothesis vs Glasp](https://tooltivity.com/extensions/compare/hypothesis-vs-glasp-web-highlighter) ### Rating Summary Hypothesis has 200,000 downloads on Chrome with a 4.12/5 rating from 223 reviews and a steady 4.05 across the last 100.  [Tooltivity](https://tooltivity.com)  gave Hypothesis a score of  **8.15/10** .  [Check out the full review here](https://tooltivity.com/extensions/hypothesis) . --- ## [7\. DocHub - Sign PDF from Gmail](https://tooltivity.com/extensions/dochub) ![DocHub signing a PDF attachment opened from Gmail](https://tooltivity.com/data/tooltivity/apps/dochub/images/gallery-image-1.webp) DocHub has a narrower job than anything else here: sign a PDF without leaving Gmail. It has 200,000 downloads and a 4.37/5 rating from 318 reviews, but the recent direction is wrong — 3.64 across the last 100, a clear slide from the all-time figure. The loop is genuinely quick. Pull a form out of a Gmail attachment, drop in your signature, send it back; no printing, no scanning, no downloading first. You can also add text, white out mistakes, fill fields, reorder pages, and save to Google Drive, and multi-signer flows with reminders work for the paperwork that needs three people. The complaints behind that 3.64 are almost all about the same thing: documents that don’t load. When it works it’s the fastest signing tool in this comparison, and that qualifier is doing real work. ### Key Features - **Sign Straight From Gmail**  – An “Open with DocHub” button on PDF attachments, no download step - **E-Signatures**  – Draw, type, or upload a signature — you can even make one on your phone - **In-Browser Editing**  – Add text and images, highlight, or white out a mistake - **Fillable Forms**  – Complete PDF form fields on screen instead of by hand - **Google Drive Integration**  – Import from Drive and save the finished file straight back - **Page Management**  – Reorder, rotate, delete, and merge pages before sending - **Multi-Signer Workflows**  – Route a document to several signers with autosave and reminders - **Templates**  – Save recurring paperwork so it doesn’t start from scratch each time ### Pros & Cons **Pros:** - Signs PDFs straight from Gmail - Free tier you can actually use - No credit card required upfront - Drive import and export - Multi-signer routing with reminders **Cons:** - Blank screens and documents that won’t load - Free plan capped per month - The Gmail flow sometimes breaks - Onboarding is clunky - Recent ratings down to 3.64 ### Who is this great for? DocHub fits anyone whose PDF life is mostly signatures — agents, freelancers, small-business owners, students returning a form. If you already live in Gmail and Drive, the workflow feels like it was built for your inbox specifically. It’s best for occasional signers who don’t want to hand over a card for a free tier. Heavy daily volume hits the monthly cap, and given the load failures in recent reviews, keep a second option installed for the day a contract refuses to open. ### Compared to others Where  [Adobe Acrobat](https://tooltivity.com/extensions/adobe-acrobat)  leans on a heavier app and a Pro plan, DocHub keeps sign-and-return inside the inbox for free.  [Smallpdf](https://tooltivity.com/extensions/smallpdf)  routes you to a web dashboard for the same job, so DocHub is the more immediate of the two for pure signing, while  [Xodo](https://tooltivity.com/extensions/xodo)  covers more editing ground without the Gmail integration. For reading and annotating a document rather than executing it, none of these are the answer. ### Detailed comparisons [DocHub vs Adobe Acrobat](https://tooltivity.com/extensions/compare/dochub-vs-adobe-acrobat)  •  [DocHub vs Smallpdf](https://tooltivity.com/extensions/compare/dochub-vs-smallpdf)  •  [DocHub vs Xodo](https://tooltivity.com/extensions/compare/dochub-vs-xodo) ### Rating Summary DocHub has 200,000 downloads on Chrome with a 4.37/5 rating from 318 reviews, though recent reviews have fallen to 3.64 across the last 100.  [Tooltivity](https://tooltivity.com)  gave DocHub a score of  **8.02/10** .  [Check out the full review here](https://tooltivity.com/extensions/dochub) . --- ## [8\. Xodo | PDF Editor, Converter & Merger](https://tooltivity.com/extensions/xodo) ![Xodo PDF tools menu with convert, merge and compress options](https://tooltivity.com/data/tooltivity/apps/xodo/images/gallery-image-1.webp) Xodo is the smallest listing in this comparison and the one with the least evidence behind it: 30,000 downloads and a 3.85/5 rating drawn from just 34 reviews, with the recent window at 3.64. With a pool that small, those two numbers are mostly the same reviews counted twice, so I leaned on hands-on testing here more than on the star count. On paper it covers a lot: edit and annotate, convert to and from Word, PowerPoint, Excel and JPG, compress, merge, crop, redact, split, rotate, and sign — free, with daily limits. In practice opinion splits hard. Some people use it happily for forms and merges. Others find it behaves more like a bookmark to Xodo’s website than an extension, which is the single most common complaint and a fair description of what happens with the heavier tools. ### Key Features - **Edit & Annotate**  – Write on PDFs, add text boxes, highlight, and underline - **Convert**  – PDFs to and from Word, PowerPoint, Excel, and JPG - **Merge & Combine**  – Join several PDFs or scans into one file - **Page Management**  – Crop, split, rotate, reorder, and delete pages - **Fill & Sign**  – Complete forms and add a hand-drawn signature - **Compress**  – Shrink oversized PDFs for email - **Redact**  – Remove sensitive text before sharing - **Fast Viewing Engine**  – Open and scroll large documents quickly, the thing Xodo has always been good at ### Pros & Cons **Pros:** - Core PDF tools genuinely free - Fill and sign forms easily - Merge, split, and delete pages - Fast, smooth viewing of big files - Decent PDF-to-Word conversion **Cons:** - Free tier has daily limits - Often behaves like a bookmark to the website - Occasional trouble opening PDFs - Editing controls frustrate - Tiny review pool, so ratings mean little ### Who is this great for? Xodo suits people who want a broad free toolkit for occasional jobs: filling a form, merging scanned pages, converting a document to Word. For light, irregular work it’s a reasonable thing to keep one click away. Go in with the right expectation and you’ll get on with it fine — this is a launcher plus a toolkit rather than a slick in-page editor, and back-to-back use will hit the daily limits. If PDF processing is a daily job, Smallpdf is worth the upgrade instead. ### Compared to others [Smallpdf](https://tooltivity.com/extensions/smallpdf)  is the cleaner, more reliable version of the same conversion-and- compression toolkit, with roughly ninety times the reviews behind it.  [Adobe Acrobat](https://tooltivity.com/extensions/adobe-acrobat)  goes much deeper for serious editing. For signing from your inbox,  [DocHub](https://tooltivity.com/extensions/dochub)  is the more focused choice. Xodo’s argument is range at no cost — and that argument holds as long as the hand-off to its website doesn’t get in your way. ### Detailed comparisons [Xodo vs Smallpdf](https://tooltivity.com/extensions/compare/xodo-vs-smallpdf)  •  [Xodo vs Adobe Acrobat](https://tooltivity.com/extensions/compare/xodo-vs-adobe-acrobat)  •  [Xodo vs DocHub](https://tooltivity.com/extensions/compare/xodo-vs-dochub) ### Rating Summary Xodo has 30,000 downloads on Chrome with a 3.85/5 rating from just 34 reviews, and 3.64 across the most recent window.  [Tooltivity](https://tooltivity.com)  gave Xodo a score of  **7.65/10** .  [Check out the full review here](https://tooltivity.com/extensions/xodo) . --- ## [9\. Diigo Web Collector - Capture and Annotate](https://tooltivity.com/extensions/diigo-web-collector) ![Diigo Web Collector toolbar with highlight and annotate options](https://tooltivity.com/data/tooltivity/apps/diigo-web-collector/images/gallery-image-1.webp) Diigo has been collecting the web for well over a decade — bookmarks, highlights, screenshots, notes, all in one library. It has 100,000 downloads and a 4.60/5 all-time rating from 2,323 reviews. The recent picture is much darker: 3.50 across the last 100, more than a full star below the average that reputation was built on. The core still works. Highlights come back on refresh, notes attach cleanly, everything syncs. What’s aged is everything around that — a dated interface, four highlight colours, a link-creation feature that misfires, and a steady run of reliability complaints. It’s a tool that stopped being maintained at the pace its users needed, and the recent ratings are the receipt. ### Key Features - **Highlighting**  – Works reliably, and highlights are recreated on refresh - **Notes**  – Attach notes to any highlight - **Link Creation**  – Link straight to a highlight, though this misfires often - **Sidebar Outliner**  – Simple layout, but it takes a while to understand - **Syncing**  – Highlights follow you across devices ### Pros & Cons **Pros:** - Highlights are recreated on refresh - Notes can be added to highlights - Cross-device syncing - Tag-based library that scales **Cons:** - Outdated design - Limited to 4 highlight colors - Link creation is unreliable - Sidebar is limited - Recent ratings down to 3.50 from a 4.60 average ### Who is this great for? Diigo makes sense if you’re already in it. Years of tagged, annotated research are a real asset, the library still holds, and there’s no urgent reason to move if it’s serving you. For anyone starting fresh, the recent slide is hard to argue past. The tag-based organisation and cross-device sync are genuinely good; the interface and the reliability are not, and both matter more on day one than they do on year ten. ### Compared to others [PDF & Web Highlighter](https://tooltivity.com/extensions/web-highlights)  covers the same highlight-and-sync ground with more colors, on-device AI, PDF annotations you can download, and no account to start.  [Glasp](https://tooltivity.com/extensions/glasp-web-highlighter)  brings the modern AI and community layer Diigo never built. And  [Weava](https://tooltivity.com/extensions/weava)  matches its folder-based research approach — the two share both the idea and the maintenance problem. ### Detailed comparisons [Diigo vs PDF & Web Highlighter](https://tooltivity.com/extensions/compare/diigo-web-collector-vs-web-highlights)  •  [Diigo vs Weava](https://tooltivity.com/extensions/compare/diigo-web-collector-vs-weava)  •  [Diigo vs Glasp](https://tooltivity.com/extensions/compare/diigo-web-collector-vs-glasp-web-highlighter) ### Rating Summary Diigo has 100,000 downloads on Chrome with a 4.60/5 all-time rating from 2,323 reviews, though recent reviews have dropped to 3.50 across the last 100.  [Tooltivity](https://tooltivity.com)  gave Diigo a score of  **7.55/10** .  [Check out the full review here](https://tooltivity.com/extensions/diigo-web-collector) . --- ## [10\. Weava Highlighter: PDF & Web](https://tooltivity.com/extensions/weava) ![Weava Highlighter extension icon](https://tooltivity.com/data/tooltivity/apps/weava/images/logo.webp) Weava closes the list, and it’s the clearest warning in it. 200,000 downloads and a 4.05/5 all-time rating from 2,754 reviews look fine until you read the recent column: 2.78 across the last 100. That’s the steepest fall of any tool here, and the only one where the current average is below three stars. The bones are still reasonable — web and PDF highlighting in several colours, notes, folders, cloud sync, automatic citations for what you highlighted. What’s dragging it under is everything around them: ads in the interface, a mandatory account, a design that stopped being updated, and a run of reviews about features breaking and support not answering. It works. It just isn’t being looked after. ### Key Features - **Web & PDF Highlighting**  – Highlight web pages and PDFs in several colors - **Annotations**  – Add notes to any highlight for later reference - **Cloud Syncing**  – Reach your highlights and notes from any device - **Organize with Folders**  – Structure research with folders and sub-folders - **Citation Creation**  – Generate citations for highlighted passages automatically ### Pros & Cons **Pros:** - Covers both web and PDF highlighting - Cloud sync across devices - Automatic citations for research **Cons:** - Interface cluttered with ads - Free version limits how much you can highlight - Account required before you start - Little sign of ongoing support or updates - Recent rating of 2.78 — the lowest in this comparison ### Who is this great for? Weava may still suit long-time users with folders of research inside it who don’t want to migrate. The highlighting and folder structure remain usable if you can look past the ads, and the automatic citations are a genuine time-saver for a bibliography. For everyone else, I’d point you elsewhere. A 2.78 average across the most recent hundred reviews isn’t a blip, and there are better-supported highlighters in this list at the same price. ### Compared to others [PDF & Web Highlighter](https://tooltivity.com/extensions/web-highlights)  does the same web-and-PDF highlighting without ads, without an account, and with a maintained interface — though Weava’s automatic citations are something we don’t offer.  [Diigo](https://tooltivity.com/extensions/diigo-web-collector)  shares the folder-based approach and much of the same ageing. And  [Glasp](https://tooltivity.com/extensions/glasp-web-highlighter)  leaves it behind on features, community, and upkeep. ### Detailed comparisons [Weava vs PDF & Web Highlighter](https://tooltivity.com/extensions/compare/weava-vs-web-highlights)  •  [Weava vs Diigo](https://tooltivity.com/extensions/compare/weava-vs-diigo-web-collector)  •  [Weava vs Glasp](https://tooltivity.com/extensions/compare/weava-vs-glasp-web-highlighter) ### Rating Summary Weava has 200,000 downloads on Chrome with a 4.05/5 all-time rating from 2,754 reviews, but only 2.78 across the last 100.  [Tooltivity](https://tooltivity.com)  gave Weava a score of  **5.67/10** .  [Check out the full review here](https://tooltivity.com/extensions/weava) . --- ## Final Thoughts Working through all ten, the first thing that stands out has nothing to do with features. Look at the recent-review column. Kami fell from 4.56 to 3.87, Diigo from 4.60 to 3.50, Weava from 4.05 to 2.78 — three tools whose reputations were earned years ago and whose current users are telling a different story. All-time ratings in this category are a record of what a tool used to be. Check the last hundred before you commit a semester to something. The second thing is that “PDF extension” describes two unrelated jobs, and most disappointment comes from picking the wrong half.  [**PDF & Web Highlighter**](https://tooltivity.com/extensions/web-highlights)  takes the top spot at 9.78/10 for the reading half: highlights that go into a searchable library, come back out embedded as real PDF annotations, and turn into flashcards, with the AI running on your own machine and no account needed to start. That’s what it’s good at. It converts nothing, compresses nothing, and signs nothing. So, honestly, by job. For the deepest, most trusted toolkit —  [**Adobe Acrobat**](https://tooltivity.com/extensions/adobe-acrobat) , if you can live with the subscription and the prompts.  [**Smallpdf**](https://tooltivity.com/extensions/smallpdf)  is the best all-rounder for converting and compressing, with  [**Xodo**](https://tooltivity.com/extensions/xodo)  as the rougher free alternative. For signing from your inbox,  [**DocHub**](https://tooltivity.com/extensions/dochub)  is faster than anything else here on the days it loads. In a classroom,  [**Kami**](https://tooltivity.com/extensions/kami)  still owns collaborative markup and voice feedback outright. And if the point of annotating is that someone replies,  [**Hypothesis**](https://tooltivity.com/extensions/hypothesis)  beats us and costs nothing —  [**Glasp**](https://tooltivity.com/extensions/glasp-web-highlighter)  is the pick if you’d rather choose your own AI model and read what others highlighted. Every tool here has a free tier, so the cheap way to decide is to install two and run the same week of real documents through both. If you mostly read PDFs,  [PDF & Web Highlighter](https://web-highlights.com/install)  is the one I’d start with — nothing to sign up for, and you’ll know within a few days whether keeping your notes in a library beats keeping them in the file. Or open the  [full comparison of all Chrome PDF extensions](https://tooltivity.com/extensions/compare/category/pdf-tools/chrome)  and weigh them side by side yourself. ## Frequently asked questions ### What is the best PDF extension for Chrome? Tooltivity ranks PDF & Web Highlighter first at 9.78/10, on a 4.83/5 Chrome rating from 4,946 reviews. But “best” depends on the job. It is built for reading, highlighting and research. For editing, converting or compressing, Smallpdf and Adobe Acrobat go much further, and DocHub is faster if all you need is a signature. ### Can I highlight a PDF in Chrome for free? Yes. PDF & Web Highlighter highlights online, local and uploaded PDFs for free, with no account needed to start. Hypothesis is free too and adds group discussion, though it requires a sign-up and gives you a single highlight colour. If you would rather not install anything, our free online PDF highlighter runs in a plain browser tab. ### Which Chrome extension can I use to sign a PDF? DocHub is the most direct option: open a PDF attachment straight from Gmail, drop in a signature and send it back, free and with no credit card upfront. Adobe Acrobat also fills and signs for free inside Chrome, and Smallpdf includes e-signing. Note that DocHub’s recent reviews have slipped to 3.64, mostly over documents failing to load. ### Is there a free alternative to Adobe Acrobat for Chrome? Smallpdf is the closest all-rounder, covering compression, conversion, merging and e-signing on a free tier, and Xodo offers similar range for free with daily limits. Neither matches Acrobat’s depth for documents that have to hold up professionally. For reading and annotating rather than editing, PDF & Web Highlighter is the free pick. ### Do my highlights stay in the PDF when I download it? With PDF & Web Highlighter, yes. Download the file from its viewer and every highlight is embedded as a real, standards-compliant PDF annotation — its own colour, notes as comments, the text still selectable — editable afterwards in Acrobat, Preview or Edge. Highlights already sitting in a PDF import back into your library with one click.