Pick by what you need
- See the answer highlighted where it is in the PDF, with no account: Onhand.
- Nothing to install, on a computer: Gemini in Chrome, which is built into the browser.
- Edit, convert and sign PDFs as well: Adobe Acrobat, with its AI Assistant.
- One sidebar with many AI models for everything you do online: Sider.
- Research papers, and finding related papers: SciSpace.
- Reading across Gmail, Google Docs, Notion and Slack too: Sidenote.
- Highlighting and keeping notes as you read: Glasp.
- A library of PDFs you chat with, on paid plans across all of them: PDF.ai.
How they compare
| What it reads | Where the answer came from | Price | |
|---|---|---|---|
| Onhand | Webpages and PDFs open in Chrome, online or on your computer, plus clearly related open tabs | Highlights the passages it used on the page, with a note in the margin beside each | Free tier with a daily limit and no account, or your ChatGPT plan or own API key; open source |
| Gemini in Chrome | The current tab, plus up to 10 open tabs on a computer; Google's help pages don't say whether it reads PDFs | Google's help pages don't describe citations for typed questions; by voice, Gemini Live can scroll to and highlight content on a webpage, but can't navigate PDFs | Free with a Google account in supported regions; you sign in to Chrome |
| Adobe Acrobat | PDFs, in Acrobat's viewer in Chrome; AI Assistant also runs in Acrobat's own apps | Citations that link to the exact locations in the document | The viewer is free; AI Assistant comes with Acrobat Studio, from US$24.99 a month, and free users get a limited number of requests |
| Sider | Webpages, open tabs and PDFs, in an all-in-one AI sidebar | Answers in the sidebar; its store listing doesn't mention highlighting the passages behind an answer | Free tier with daily credits; paid plans from US$10 a month |
| SciSpace | Papers, articles and PDFs on most sites in Chrome | A citation with each answer, with the location of the source | Extension free to install; paid plans from US$12 a month billed yearly, or US$20 monthly |
| Sidenote | Webpages, PDFs, YouTube, Gmail, Google Docs, Notion and more, after you sign in | Citation chips; click one and the page scrolls to the sentence and highlights it | Free plan with monthly limits; paid plans from £10 a month |
| Glasp | PDFs open in the browser, or uploaded to your Glasp library; it also highlights webpages | Answers cite the pages they came from, and your own highlights are used as context | 20 PDF chat messages a month free; Pro is US$15 a month, or US$12.50 billed yearly |
| PDF.ai | PDFs opened in Chrome, including files on your computer and in Dropbox or Google Drive | Not described on its extension or pricing pages | Free plan with 1 PDF and 100 questions a month; Pro is US$10 a month billed yearly |
Details are from each tool's own pages and store listings, checked November 2, 2026: Google's Gemini in Chrome and Gemini Live help pages; Adobe's AI Assistant, help and pricing pages; Sider's store listing and pricing; SciSpace's extension and pricing pages; Sidenote's website and pricing; Glasp's PDF chat and pricing pages; and PDF.ai's extension and pricing pages. Prices are in the currency each tool lists and can change. Product names are trademarks of their owners; Onhand isn't affiliated with any of them.
What to check before you pick
- Where you read: some tools work on the PDF you already have open in Chrome; others open it in their own viewer or ask you to upload it to their library first.
- Whether you can check the answer: a page number tells you where to look; a highlight on the passage itself shows you the evidence in context.
- What the free use covers: free plans are counted per day, per month or per document, and some cover only part of the features.
- Whether you need an account: most of these tools need one, even on a free plan.
Where Onhand fits
Onhand is built for close reading: you ask about the PDF or webpage you have open, and it highlights the passages it used right there, so you can check each one in context. Learning mode adds guiding questions and quizzes tied to the page. It's a browser extension, so there's no phone app, and it doesn't edit or sign PDFs or keep a library of uploaded files; if you need those, one of the other tools fits better.
Try it
Add Onhand to Chrome, open a PDF, and click the Onhand icon or press
Ctrl+Shift+Space (⌘+Shift+Space on a Mac).
Onhand Free needs no account or API key and has a daily limit; you
can also sign in with your ChatGPT plan or use your own OpenAI,
Anthropic, Google Gemini or OpenRouter key.