Compare PDF Files Online — Free & Private
Drop two PDFs and see every change highlighted instantly. SnapTextCompare extracts text from each PDF locally in your browser and diffs it word by word — no upload, no signup, no fee. Built for legal, finance, academic and engineering teams that can't ship sensitive PDFs to a third-party server.
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Why Compare PDFs in Your Browser?
SnapTextCompare extracts PDF text and compares it locally in your browser. Other products offer different web and desktop workflows; processing location depends on the product and feature. Compare privacy policies and document capabilities rather than assuming all PDF tools upload files.
That also makes it fast: there's no upload step, no queue, no rate limit. Drop the file, see the diff.
PDF Comparison Use Cases
Legal redlines. Compare a draft and the counterparty's revised contract to verify only negotiated terms were touched.
Policy & compliance. Diff successive versions of a regulatory policy PDF to write a clean change log.
Academic papers. Compare a submitted and a revised manuscript to track reviewer-requested edits.
Engineering specs. Diff two versions of a datasheet, RFP or technical specification before quoting or shipping.
Financial reports. Compare two PDF financial statements to spot adjustments between drafts.
How It Works
1. Parse. Both PDFs are read with Mozilla's pdf.js, page by page, in the browser.
2. Tokenize. Extracted text is normalised and tokenised by word or by line.
3. Diff. A Myers-style diff algorithm computes additions and deletions.
4. Render. Results are highlighted inline — green for added, red for removed — with character-level precision on changed words.
Limitations & Tips
Scanned PDFs: Image-only PDFs need OCR first (try Tesseract or Adobe Acrobat's "Recognize Text"), then bring the text here.
Very large PDFs: Performance depends on your device and text volume. Compare smaller sections if the page slows down.
Reading order: Columns, tables, hyphenation and missing text layers can produce incomplete extraction. Verify the extracted text against both original PDFs before approving changes.
Layout changes: SnapTextCompare diffs the extracted text stream, not visual layout. For visual layout diffs use a graphical tool.
Related comparison tools
How SnapTextCompare compares PDF files
Diff engine
Google's diff-match-patch (Apache 2.0), running in your browser. Character mode diffs raw characters; word and line modes encode tokens or lines first and diff those, then decode the result.
Similarity & importance
Similarity = 1 − Levenshtein / max(len). Importance weighs each change by category — money and dates score 90+, punctuation scores 3. Fixed rules classify a given diff; they do not determine meaning or whether an edit is safe.
Privacy
Files are read with the HTML5 File API and processed in your browser. No network request is ever made with your content — verifiable in the Network tab of your browser's DevTools. Full recent comparisons are saved in this browser's local History, even after closing the tab. Clear History to remove them.
PDFs are parsed with Mozilla's pdf.js in your browser, page by page, text-layer only. Scanned PDFs need OCR first. Columns, tables, reading order and hyphenation can affect extraction; check the extracted text against the original PDF. Visual layout is not compared.
PDF Comparison FAQ
Common questions about comparing PDF files online.