Each page is rendered and compared; pixels that differ are painted red over a faint copy of the original.
Files never leave your device.How it works
How to compare PDFs
- 1Add the original PDF, then the changed PDF.
- 2Click Compare.
- 3Download the difference images — one per page, changes marked in red.
Frequently asked questions
- How does it detect changes?
- Each page of both files is rendered to an image and compared pixel by pixel. Pixels that differ are painted red over a faint grayscale of the original, so changes jump out.
- Does my file get uploaded?
- No. Both PDFs are rendered and compared entirely in your browser — nothing leaves your device.
- What if the files have different page counts?
- Extra pages are compared against a blank page, so pages that were added or removed show up as fully changed.
See exactly what changed
When someone sends back a revised PDF, it's tedious to hunt for what moved. Compare PDFs renders both files and overlays them: every pixel that differs between the two versions is painted red over a faded copy of the original, so edits, moved text, and added or removed content are obvious at a glance.
Visual, page by page
The comparison is visual rather than text-based, so it catches layout and image changes as well as text. You get one difference image per page. Where the two files differ in length, the extra pages are compared against blank, marking them as wholly changed.
Notes and limits
Both files are processed locally — nothing is uploaded, which matters when you're diffing confidential drafts. The output is images highlighting differences, not an edited PDF.
Why pixel comparison instead of text diffing
Text-diffing tools work by extracting a document's text and comparing strings, which misses anything that isn't text — a moved image, a shifted table border, a change in font or color, a logo that got swapped out. Compare PDFs renders each page as it actually looks and compares the rendered pixels, so it catches layout and visual changes a text diff would silently pass over, at the cost of not producing a word-level "this sentence changed" report.
Where this earns its keep
It's most useful for contract redlines where a single number or clause matters, catching accidental formatting drift between "final" and "final_v2" of a design document, or confirming a vendor actually applied the revisions you asked for rather than re-sending the same file with a new name.
What can look like a false positive
Re-exporting a PDF from different software, even with identical content, can shift anti-aliasing or font hinting by a pixel or two and paint faint red noise across a page that didn't meaningfully change — worth a quick eyeball before assuming real edits happened. For turning either file into standalone images for a closer look outside the diff view, use PDF to JPG; if you need to reassemble a corrected version afterward, Organize PDF can rebuild the page order.