How to use
- Select PDF A and PDF B using the two file pickers.
- Click Compare to render and diff every page.
- Review each page: changed areas appear in red with the percent changed shown.
- Check the flags for any page that exists in only one of the two PDFs.
Frequently asked questions
How are the two PDFs compared?
Each page of both files is rendered to an image and compared pixel by pixel. Pixels that differ beyond a small threshold are painted bright red over a faded grayscale copy of PDF A, so the changes stand out. This is a visual diff, not a text or word-level comparison.
Are my PDF files uploaded anywhere?
No. Both PDFs are read and compared entirely in your browser using pdf.js — nothing is sent to a server and nothing is uploaded, so even confidential documents stay private on your device.
What do the red areas and the percentage mean?
Red marks the parts of the page that differ between the two PDFs. The percentage is the share of that page's pixels that changed, giving you a quick sense of how much was altered.
What happens if the two PDFs have a different number of pages?
Pages are matched by number. Any page that exists in only one file — for example an extra page at the end — is flagged as present in only PDF A or only PDF B so no change is missed.
Does it detect text changes, or does layout shift break the comparison?
Because the diff is visual, any change to text, images, or layout shows up in red. Note that a shift in position or reflow can highlight large areas even when the wording is similar, since pixels no longer line up.
Is there a file size or page limit?
There is no fixed limit, but everything runs in your browser, so very large PDFs with many pages take more time and memory. If the tool reports an error, try comparing smaller or password-free PDFs.
About this tool
Free online PDF compare tool to spot differences between two PDFs page by page. Runs 100% in your browser, highlights changes in red, no uploads.