How to compare two versions of a PDF and see exactly what changed

“Here is the revised version — only a couple of small changes.” Anyone who has signed a contract, approved a policy or checked a resubmitted report has heard that sentence. Reading both versions side by side is slow and unreliable; the eye skips over a changed date or a missing “not”. A text comparison finds every difference in seconds.

When it is worth comparing

• A revised contract or lease before you sign it.
• An updated policy, terms of service or handbook, to see what actually changed.
• A report or thesis returned after edits, to check every change was intended.
• Two copies of a document that should be identical, to confirm they are.

Even when the other side has listed their changes, a comparison is a useful check. Edits get forgotten in a summary far more often than anyone admits.

Compare two PDFs step by step

1. Open Compare Two PDFs.
2. Add the original document on the left and the revised one on the right.
3. Press Compare. Both files are read page by page.
4. Work through the pages that changed. Added lines are marked with a plus, removed lines with a minus and a strike-through, as well as with colour.
5. Download the comparison as a text file if you need to send it on or keep a record.

Both documents are read in your browser and neither is uploaded — which matters when the files are contract drafts or confidential reports.

How the comparison works

The text of each page is extracted from both documents and matched using the same method version-control software uses to compare code. It finds the smallest set of additions and deletions that turns one version into the other, so a paragraph inserted at the top does not make every line after it look changed. Pages with no differences are left out of the report, so what remains is only what matters.

Reading the results

• A changed word shows as a removed line and an added line. Look at the pair together to see exactly which word moved.
• A moved paragraph shows as a removal in one place and an addition in another. If the same text appears on both sides, nothing was rewritten, only relocated.
• A warning about page counts means a page was added or removed. Content after that point can legitimately appear changed, so start reading from the first real difference.

What a text comparison cannot see

Only the words are compared. That has some consequences worth knowing:

• Layout, fonts and colours are ignored. A document redesigned with the same wording reports no differences.
• Pictures are not compared. A changed figure in a chart, a swapped signature image or an edited table that is embedded as a picture will not show up.
• Scanned pages have no text to compare. If one version is a scan, run it through Image to Text (OCR) first, or compare the scan by eye.

For anything important, combine the comparison with a quick look at the pages that carry figures and signatures.

Tips for reliable comparisons

• Compare the exact files. Make sure the “original” really is the version you agreed to, not a later draft.
• Expect noise from re-exports. A document saved from a different program can break lines differently. Changes in line breaks alone may show as lines removed and added with the same words.
• Check the numbers twice. A changed amount, date or percentage is a one-character difference that is easy to skim past in a long report.

Comparing Word documents

If you have both versions as Word files, Word's own Compare feature shows changes in place with formatting. If you only have PDFs, or one side is a PDF, compare the PDFs. To get the full text of a single document for searching or quoting, PDF to Text extracts it page by page.