How is this different from other online PDF tools?

Most online PDF tools send your files to a remote server for processing. This tool processes everything locally in your browser using client-side JavaScript. Your files are never transmitted to any server, which means your document content stays entirely under your control.

Are my PDF files uploaded?

No. Your files are read directly by your browser. Your files are never transmitted over the network. The tool works entirely within the browser tab you have open.

Can I verify that files are not uploaded?

Yes. Open your browser's developer tools (F12), go to the Network tab, and watch for any outgoing requests while using the tool. You will see no file data leave your browser. The site may record an anonymous page-view count, which never includes your files and can be disabled.

Does this tool work offline?

Yes, once the page has loaded the tool processes your files entirely in your browser; tool functionality needs no network connection. You can disconnect from the internet and continue using it.

What happens when I refresh the page?

Because nothing is stored on a server, refreshing the page clears your current session. Any files you had selected will need to be selected again.

Does this tool store my files?

No. Files are held in browser memory only for as long as the page is open. Closing or refreshing the page discards them. Nothing is written to disk by the tool, and nothing is sent to a server.

Can this tool unlock password-protected PDFs?

No. This tool does not attempt to remove or bypass PDF password protection. If you know the password, the Unlock PDF tool on this site can remove it locally; then this tool can process the file.

What technologies does this tool use?

This tool uses pdf.js (Mozilla's client-side PDF engine) to render both documents in a Web Worker and the Canvas API to compare them pixel by pixel — all within your browser.

Does this tool use WebAssembly?

No. pdf.js is a plain JavaScript library — it does not use WebAssembly. All rendering and comparison happens in client-side JavaScript within your browser.

How do I compare two PDFs with this tool?

Pick your first PDF in the top panel and your second PDF in the panel below, both directly from your device, then press the Compare button. Each page pair is rendered and checked in your browser, and you get a per-page summary with the differing areas highlighted in red, all without anything leaving your tab.

Why are two PDFs that look the same to me reported as different?

The comparison is visual rather than text-aware: it renders each page and checks the pixels, so things like a different font rendering, a shifted image, or another scan resolution of the same document can register as changed even when the wording matches. A small per-channel tolerance absorbs anti-aliasing and rounding noise, but larger visual shifts still show up as red regions with a change percentage.

What happens when one PDF has more pages than the other?

The tool compares up to the larger page count, so every page that exists in only one of the two files is reported as fully changed (100%) rather than skipped. This makes added or removed pages easy to spot at the end of the per-page list.

Does Compare PDFs cost anything to use?

Compare PDFs is completely free — no account, no sign-up, and no cap on how many document pairs you compare — and it always will be. Both PDFs are rendered and diffed pixel by pixel right inside your browser tab using pdf.js and the Canvas API, so your files never leave your device; nothing is uploaded or sent to any server.

Compare Two PDFs Privately — Spot the Differences in Your Browser

Select two PDFs; each page pair is rendered and compared pixel by pixel in your browser, with differences highlighted in red and a per-page change percentage.

Quick answer

What it does: Select two PDFs; each page pair is rendered and compared pixel by pixel in your browser, with differences highlighted in red and a per-page change percentage.
Free?: Yes — 100% free, no account or sign-up.
Files uploaded?: No — everything is processed in your browser.
Works offline?: Yes — once the page has loaded.
Best for: A lawyer checks a contract the other party returned to spot any last-minute edits before both parties sign.
Good to know: The comparison is visual: it detects what looks different when rendered, not the underlying text edits — moved paragraphs show as changed regions.

How it works

Select the two PDF files you want to compare from your device.
Both files are read into browser memory — no data leaves your browser.
pdf.js renders each page of both documents to canvases in a Web Worker.
Each page pair is compared pixel by pixel; differing areas are painted red over a faded copy of the page.
A per-page summary shows how much changed, with a highlighted preview for every differing page.

When to use this tool

A lawyer checks a contract the other party returned to spot any last-minute edits before both parties sign.
An editor confirms that only the approved corrections appear between an original manuscript PDF and the final revised proof.
A QA engineer verifies a newly generated report PDF matches a known-good reference output, page by page, with red highlights.
Comparison is visual (pixel-level), not a text diff — reflowed text may show as fully changed even if the words are identical.

Frequently asked questions

How is this different from other online PDF tools?: Most online PDF tools send your files to a remote server for processing. This tool processes everything locally in your browser using client-side JavaScript. Your files are never transmitted to any server, which means your document content stays entirely under your control.
Are my PDF files uploaded?: No. Your files are read directly by your browser. Your files are never transmitted over the network. The tool works entirely within the browser tab you have open.
Can I verify that files are not uploaded?: Yes. Open your browser's developer tools (F12), go to the Network tab, and watch for any outgoing requests while using the tool. You will see no file data leave your browser. The site may record an anonymous page-view count, which never includes your files and can be disabled.
Does this tool work offline?: Yes, once the page has loaded the tool processes your files entirely in your browser; tool functionality needs no network connection. You can disconnect from the internet and continue using it.
What happens when I refresh the page?: Because nothing is stored on a server, refreshing the page clears your current session. Any files you had selected will need to be selected again.
Does this tool store my files?: No. Files are held in browser memory only for as long as the page is open. Closing or refreshing the page discards them. Nothing is written to disk by the tool, and nothing is sent to a server.
Can this tool unlock password-protected PDFs?: No. This tool does not attempt to remove or bypass PDF password protection. If you know the password, the Unlock PDF tool on this site can remove it locally; then this tool can process the file.
What technologies does this tool use?: This tool uses pdf.js (Mozilla's client-side PDF engine) to render both documents in a Web Worker and the Canvas API to compare them pixel by pixel — all within your browser.
Does this tool use WebAssembly?: No. pdf.js is a plain JavaScript library — it does not use WebAssembly. All rendering and comparison happens in client-side JavaScript within your browser.
How do I compare two PDFs with this tool?: Pick your first PDF in the top panel and your second PDF in the panel below, both directly from your device, then press the Compare button. Each page pair is rendered and checked in your browser, and you get a per-page summary with the differing areas highlighted in red, all without anything leaving your tab.
Why are two PDFs that look the same to me reported as different?: The comparison is visual rather than text-aware: it renders each page and checks the pixels, so things like a different font rendering, a shifted image, or another scan resolution of the same document can register as changed even when the wording matches. A small per-channel tolerance absorbs anti-aliasing and rounding noise, but larger visual shifts still show up as red regions with a change percentage.
What happens when one PDF has more pages than the other?: The tool compares up to the larger page count, so every page that exists in only one of the two files is reported as fully changed (100%) rather than skipped. This makes added or removed pages easy to spot at the end of the per-page list.
Does Compare PDFs cost anything to use?: Compare PDFs is completely free — no account, no sign-up, and no cap on how many document pairs you compare — and it always will be. Both PDFs are rendered and diffed pixel by pixel right inside your browser tab using pdf.js and the Canvas API, so your files never leave your device; nothing is uploaded or sent to any server.