How to use it
- Choose the old version in the first box and the new version in the second. Each file's page count appears under its name.
- Click Compare the text. Both files are read page by page in your browser.
- Read the four counts at the top: lines added, lines removed, lines unchanged and pages changed.
- Look at each changed page: a green line is in the new version only, a red line is in the old version only. Unchanged lines around a change are shown for context.
How the lines are compared
Each page's text is taken from the PDF, one line per line of text. Spaces inside a line are made into single spaces and empty lines are dropped, so a change in the spacing alone does not count. The page at the same position in each file is compared with the other; a page that exists in only one file is compared with an empty page.
The comparison finds the fewest added and removed lines that turn the old text into the new. A paragraph that moved shows as removed in one place and added in another.
What is not compared
Only the text is read. Pictures, colours, the position of text on the page, fonts and form values are not compared, and a changed word inside a line appears as the whole line removed and added.
A scanned page is a picture with no text to read, so it cannot be compared. The tool tells you which file has no text.
- Text is read as the PDF stores it; a PDF whose text is drawn in an unusual way may come out in a different order.
- Very different pages are shown as all lines removed and all added, which is correct but not the shortest list.
Example: a contract, version 1 and version 2
Version 1 of a contract says the payment is due in 30 days. Version 2 says 45 days, and adds one new clause on page 3.
The result shows on page 2 one line removed (the old sentence) and one line added (the new sentence), and on page 3 one line added for the new clause, with the unchanged lines around them.
Frequently asked questions
Are my PDF files uploaded anywhere?
No. Your browser reads the text of both files and compares it on your own device. Nothing is sent to our server.
Why does a changed word show the whole line as changed?
The comparison works line by line, so one changed word makes its line appear as removed and added again. Read the two lines side by side to see the word.
Why does the tool say a file has no text?
The file is probably a scan, which is a picture of the pages. A picture cannot be compared as text. Use a PDF with real text, or run text recognition on the scan first.
Why do the pages have different numbers of lines?
Lines are the lines of text the PDF stores, so a different line break or a moved paragraph changes the count. The page summary shows how many lines were added and removed on each page.
Does it compare pictures or the layout?
No. It compares the text only. Use a visual comparison tool to find changes in pictures or in the layout of the pages.
Does it work on a phone?
Yes. Choose both files, tap Compare the text and scroll through the pages. Large files take longer on a phone.
Sources
- pdf.js, the open-source library that reads the text of each page in your browser
- Myers, E. W. (1986): An O(ND) Difference Algorithm and Its Variations, the basis of the line comparison
Figures and text last checked on Tuesday, November 10, 2026.