PDF Diff & Comparison Tool
Upload two PDF files to compare their text content — mismatches, additions, and removals highlighted word-by-word.
About this PDF Comparison Tool
This free PDF diff tool extracts the text content from two PDF files and compares them word-by-word and line-by-line — right in your browser. It uses PDF.js for extraction and a Longest Common Subsequence (LCS) algorithm for precise word-level diffing. Your files are never uploaded to any server.
It is ideal for comparing contract revisions, legal document versions, academic papers, reports, or any two PDFs where you need to quickly spot what changed.
Features
- Word-level highlighting — Changed words are highlighted individually, not just entire lines.
- Side-by-side view — See both documents in parallel columns for quick scanning.
- Unified view — See all changes in a single column with old/new labels.
- Similarity score — Instantly know how alike the two PDFs are as a percentage.
- Show/hide unchanged — Focus only on differences, or toggle to see all lines.
- 100% private — PDF text is extracted locally in your browser using PDF.js. No file upload, no server.
Frequently asked questions
What kinds of PDFs can I compare?
This tool works best with text-based PDFs — documents created in Word, Google Docs, or exported from web pages. Scanned PDFs (image-only) contain no embedded text and will show empty results; you would need OCR software for those.
Is my PDF uploaded to a server?
No. PDF text extraction runs entirely in your browser using the open-source PDF.js library. Your files never leave your device.
Why does the comparison show false differences?
PDFs encode text in visual order (page position), not logical reading order. If a paragraph reflows between versions, lines may shift even if content is identical. This is a limitation of PDF text extraction, not the diff algorithm.
What does the similarity score mean?
The similarity percentage is calculated as the proportion of unchanged lines relative to the total number of lines across both documents. A score of 100% means the extracted text is identical.
Can I compare large PDFs?
Yes, but performance depends on your device. For very large PDFs (100+ pages), extraction may take a few seconds. The diff itself is fast even for thousands of lines.