Compare Two PDFs — Visual Diff
Add two PDFs and see exactly what changed. Each page is rendered and compared pixel by pixel; differences are painted red over a faded copy of the original, with the count and percentage per page — and a PNG you can download for the ticket.
Drop exactly two PDFs here
First file = original · second = revised
Need test files? Grab sample-10-pages.pdf and a modified copy from the sample library.
Visual, not textual
This compares appearance. Both files are rasterised at the same resolution and every pixel is checked, so it catches things a text comparison cannot: a moved logo, a changed chart, different spacing, a font substitution, a colour change, a stamp added. For wording changes in a contract, PDF text diff is the sharper tool — it reports added and removed lines instead of red pixels.
Using both is the reliable approach for a document review: the text diff tells you what the words say now, the visual diff tells you whether anything else moved.
Reading the result
- Red pixels are where the two pages differ by more than the tolerance.
- The faded grey underneath is the first file, kept at low contrast so you can see where on the page the change sits.
- The percentage is the share of the page area that differs — a useful triage number: below about 0.1% is usually a rendering artefact, a few percent is a real edit.
- Pages present in only one file are reported as such, so an inserted or deleted page does not look like a hundred percent change on every page after it.
Tuning DPI and tolerance
Higher DPI catches finer differences and costs memory and time — 96 is a good default, 150 for small print, and 48 for a fast sanity check on a long document. Tolerance sets how different two pixels must be before they count: raise it to about 20–30 if antialiasing noise is producing a light red haze over unchanged text, and drop it to 0 for an exact comparison.
FAQ
Why do identical-looking pages show tiny differences?
Antialiasing. Two PDFs that produce the same visible page can rasterise a fraction differently, especially after a re-save. Raise the colour tolerance to 20–30 and the noise disappears while real changes stay.
Can it compare files with different page counts?
Yes. Pages that exist in only one file are listed separately rather than being diffed against nothing — so an inserted page does not cascade into every later page showing as changed.
Does it detect moved paragraphs?
It shows them as differences in both the old and new position, because the pixels changed in both places. A text diff aligns content and calls it a move; the visual diff cannot.
How large a file can it handle?
It renders one page pair at a time, so page count matters less than page size. A hundred A4 pages at 96 DPI is comfortable on a normal laptop; drop the DPI for very long documents.
Are my documents uploaded?
No. Both files are rendered and compared in this page — which matters, since the usual reason to compare two PDFs is that they are contracts or drafts.
Related tools
- PDF text diff — compare the words, not the pixels
- PDF to images — export the pages yourself
- PDF inspector — compare structure and metadata
- PDF metadata — check which file is newer
- Font checker — diagnose a font substitution