Compare PDFs
Compare two PDFs and see every changed word.
Pick the original and the revised version. The differences appear below, page by page, with insertions and deletions marked. Neither file leaves your computer.
- Neither PDF is uploaded
- Word-level differences
- Inserted and deleted pages handled
- Free for 5 pages each
PDF comparison tool
Original (A)
No file yet
Revised (B)
No file yet
No upload. This page's security policy forbids network connections, so your file cannot leave it. See how to check that yourself.
Free: on-screen comparison of the first 5 pages of each file. Pro ($19, once): every page, and a downloadable redline PDF with the changes marked. Only the text of the PDFs is compared, not images or layout.
How it works
Choose both versions
Pick the original as A and the revised document as B. Or press Try sample contracts to see an example.
Read the differences
The summary shows words added and removed, and which pages changed. Switch between side by side and inline, and hide pages that did not change.
Share a redline (Pro)
Download a PDF report with the changes marked in red and blue, ready to attach to an email.
What the comparison shows
For every pair of matched pages you see the same text twice in side-by-side view: on the left what was removed from A, on the right what was added in B, with unchanged words in between. Inline view merges them into one flow, with removed words struck through and added words underlined.
Original (A)
Coffee costs 5 dollars. Cake is free on Friday. We close at five.
Revised (B)
Coffee costs 6 dollars. Cake is free on Friday and Saturday. We close at six.
Invented example. In the tool, "5" shows as removed and "6" as added, "and Saturday" as added, and "five" and "six" as a removal and an addition.
How pages are lined up
Comparing page 1 to page 1 and page 2 to page 2 goes wrong the moment someone inserts a page. This tool first matches pages by the words they share, using a similarity score, and only then compares matched pages word by word. A page that has no partner is reported as wholly added or wholly removed.
Limits you should know
- Only the text layer is compared. A changed image, chart or signature is not seen.
- No OCR: scanned documents have no text to compare.
- Text that moves across a page break appears as a removal and an addition.
- Very large documents take a few seconds; everything is computed on your device.
Questions
Are my PDFs uploaded anywhere?
No. Both files are read by code running in your browser tab, and the page's Content-Security-Policy forbids network connections. The Network tab in your browser's developer tools stays empty while you compare.
How does the comparison work?
Text is extracted from every page of both files with pdf.js. Pages are matched up by how much of their wording they share, so an inserted or deleted page does not push every later page out of line. Matched pages are then compared word by word, and pages with no partner are reported as added or removed.
What does it not compare?
Images, drawings, fonts, colours, spacing and page layout. Only the words. If a clause moves from the bottom of one page to the top of the next, it shows as removed on one page and added on the other.
Can it compare scanned PDFs?
Not in this version. A scan has no text to extract and there is no OCR. The page tells you when a file has no text.
Why does a long document show many differences?
Different tools export the same document with different line breaks, hyphenation and headers. The comparison ignores line breaks and spacing, but running headers and page numbers are words like any others and show up as changes when they differ.
What is the redline PDF?
A Pro feature. It downloads a PDF report with a summary and, for each changed page, the text with removed words in red with a strike-through and added words in blue with an underline. Long unchanged stretches are collapsed to a word count. Characters outside the standard Western character set print as question marks in the report.
What is free and what is Pro?
Free: on-screen comparison of the first 5 pages of each file. Pro, one payment of $19 that also covers the redaction tool: every page and the redline PDF.