How to compare two PDFs
- Load both files. The original goes on the left, the changed version on the right.
- Click Compare PDFs. Both documents render, then get compared page by page.
- Review the differences. Each page appears three times: original, changed, and the differences with every altered area in red. A summary lists the pages that differ.
A visual diff of every page
Checking two versions of a contract by eye is slow, and the moved paragraph or the changed digit is what slips past you (Xerox scanners once did this). Sleek PDF renders both files and overlays them pixel for pixel, so anything that altered a page lights up red. Being visual rather than text-based, it copes with scans and image-heavy PDFs that a text diff would choke on. And it all happens locally, so confidential drafts stay that way.
Getting a clean comparison
A pixel diff reports everything that changed the rendered page, including things you may not care about. If one version was re-exported from Word and the other from a print driver, fonts can rasterise a hair differently and whole paragraphs glow red even though no word changed. The fix is to compare like with like where you can, two exports from the same source, or two scans from the same machine. Rotated or resized pages likewise read as wholesale change; straighten the rotation or match the page sizes first and the noise drops away.
When the two files are text-born and what you want is the wording rather than the look, a text comparison can serve better: extract the text from both and hand the two files to any diff or track-changes tool. The visual diff here answers a different question, "does anything about these pages look different", which is the question that matters for signatures, stamps, scans and layouts.
Common uses for comparing PDFs
- Compare contract versions: every change between two drafts of an agreement, marked in red.
- Check a proof: confirm the revised layout matches what you signed off on.
- Find edits in a report: see exactly what moved between two versions.
Frequently asked questions
How do I compare two PDFs and see what changed?
Original on the left, changed version on the right, then click Compare. Sleek PDF renders both and lays out every page three ways: original, changed, and a “Differences” image with each altered area in red. A summary tells you which pages differ.
Does it compare the look of the pages or the text?
The look. It is a pixel comparison, so it catches anything that changed how a page looks: edited text, a moved image, a new stamp, a shifted layout, a different colour. It also works on scans and image-based PDFs, where text extraction gets you nothing.
What if the two files have a different number of pages?
Pages that exist in only one file get flagged as added or removed, so you can see where content was inserted or dropped.
Is there a page limit?
The first 30 pages. Comparison renders both documents in full, and that is roughly where memory starts to hurt. Split longer documents into sections first.
Are my PDFs uploaded to compare them?
No. Both files are rendered and diffed inside the browser. Useful, given that what people usually compare is two drafts of the same contract.