Free PDF Compare
Compare PDF pages visually and by extracted text, then export difference images and reports.
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How to compare PDF pages and inspect visual differences
Use page-pair comparison to inspect revisions without uploading documents. Visual highlights and extracted-text findings complement each other, but neither replaces careful review.
- Choose the original and revised PDFs, supplying passwords when required.
- Select equal-length page ranges or compare the first ten common pages.
- Choose rendering width, pixel threshold, alignment and margins, then run comparison.
- Review both page images, red difference highlights and extracted text, then download the report.
When a page-by-page PDF comparison helps
A contract comes back from the other side with a note that says only minor edits. A designer sends version three of a brochure. A supplier reissues a price sheet with the same file name. In each case you need to know what moved on the page, not just whether the file changed.
This tool suits paralegals checking a returned agreement, print buyers proofing a revised layout, teachers comparing two versions of a worksheet, and anyone reviewing a policy update. Because both files are opened in your browser, it also fits documents you would rather not send to an online service.
A worked example with an inserted cover page
Say the original report has 12 pages and the revised report has 13, because a new cover was added at the front. If you leave both page fields blank, the tool pairs page 1 with page 1, page 2 with page 2, and so on, and almost every pair will look different. Instead, type 1-10 for the original and 2-11 for the revised file. Now each original page is matched with its true counterpart.
Keep the default 900 px width and the physical-scale alignment. A US Letter page is 612 by 792 points, so it renders at 900 by 1,165 pixels. With outer margins set to 5 percent, the tool skips a 45-pixel band on each side and a 58-pixel band at the top and bottom, which leaves 810 by 1,049, or 849,690 pixels, to compare. If 8,497 of those pixels differ by more than the threshold, the pair heading reads 1% changed pixels.
Each pair then shows the original image, the revised image and a third image where unchanged content is faded to light gray and changed pixels are painted red.
How the visual and text checks work
For the visual check, both pages are drawn onto a white canvas at the same size. For every pixel, the tool takes the largest difference across the red, green and blue channels. If that difference is above the threshold you chose, from 0 to 100 on a 0 to 255 scale, the pixel counts as changed. The percentage is changed pixels divided by compared pixels, rounded to two decimals.
For the text check, the tool pulls the text layer from each page, optionally lowercases it and collapses whitespace, then compares the two strings. It also lists words that were added or removed with counts, such as net (2). These are word tallies, not a sentence-by-sentence redline, so a reordered paragraph can show no added or removed words at all.
You can save a PDF report with one page per pair, a JSON report with settings and text findings, or a PNG difference image for any single pair.
Common mistakes to avoid
The most frequent error is comparing pages that do not correspond, which floods the result with red. Check the page count of each file first and offset the ranges when pages were inserted or deleted. Both ranges must contain the same number of pages, and a single run handles at most ten pairs.
Another mistake is setting the threshold to 0. Anti-aliasing and slight font differences then mark many pixels as changed even when nothing meaningful moved. Start near the default of 25 and lower it only when you are hunting for faint color shifts. Finally, do not treat a text match as proof that two pages are the same, and remember that scanned pages have no text layer for the tool to read.
Useful tips and limitations
- Pair different page numbers when a revised document has an inserted cover page.
- Font rendering and page alignment can create pixel differences. Scanned documents need visual review because OCR is not performed.
- Use the Fit both pages to the same width alignment when one file was exported at A4 and the other at US Letter, so content lines up instead of shifting.
- Raise the outer margin setting to skip page numbers, dates or headers that you already know will differ between versions.
Common questions
Does matching PDF text mean the pages are identical?
No. Text extraction can miss images, scans and layout changes. Review the visual comparison as well as extracted text.
Can I compare every page of a long PDF at once?
This tool compares up to ten page pairs per run from documents up to 500 pages. Select additional ranges for subsequent runs.
What does the red overlay on the difference image mean?
Red marks pixels whose color changed by more than your threshold. Everything else is shown as a faded gray copy of the original page so you can see where each change sits.
Can I compare password-protected PDFs?
Yes. Enter the password for each file in its own field before you run the comparison. The password is used only to open the file in your browser.
Is there a file size limit?
Yes. The two PDFs together can total up to 60 MB, and each document can have up to 500 pages.
PDF parsing, rendering and comparison occur locally. Reports can include extracted document text; share them carefully.