How to compare two PDF files and see every change

Three ways to compare PDFs

• By eye, side by side: fine for one page, risky for anything longer.
• Convert both to Word and use Word's Compare feature: works for simple text, but conversion can introduce differences of its own and loses layout.
• A PDF comparison tool: compares the documents directly and lists every difference in text, formatting, pages and pictures. This is the reliable option for contracts, legal documents and drawings.

How to compare two PDF files in PDFZyro

1. 1Open Compare and choose the older and the newer version. They can be two different files, or two versions of the same document in your library.
2. 2Start the comparison. It runs in the background, so you can keep working; documents of up to 500 pages are supported.
3. 3Review the result side by side, with both documents scrolling together. Changes are highlighted in both versions.
4. 4Use the list of differences to step through each change, and filter it by text, formatting, pages or visual changes. The N and Shift+N keys move to the next and previous difference.
5. 5Download a report of every difference to share with a colleague, a client or your lawyer.

What a good comparison finds

• Added, removed, changed and moved text.
• Formatting changes: font, size, weight, slant and colour. In a contract, a clause made smaller or lighter can matter.
• Pages that were added or removed.
• Changes in pictures and layout, found by comparing the rendered pages, which also catches changes in drawings and scans.

Comparing scanned PDFs

A scan has no text a computer can read, only a picture of it. The visual comparison still finds what changed on the page. To compare the words themselves, make both scans searchable with OCR first, then compare.

Tips for comparing contracts and legal documents

• Always compare the version you're about to sign with the last version you agreed, not only the drafts in between.
• Look at formatting and page changes as well as text: moved clauses and changed numbering are easy to miss.
• Keep the comparison report with your records of the negotiation.
• Compare signed copies against the final draft before filing them.

Why comparing PDFs is harder than comparing Word files

A Word document stores paragraphs. A PDF stores text placed at exact positions on a page, often line by line, sometimes word by word. When a sentence is added near the top of a page, every line below it moves, and a simple comparison reports the whole page as changed.

A good PDF comparison rebuilds the reading order first, then matches the text of the two versions, so it reports the sentence that was added rather than everything that moved. It also compares how pages look, which catches changes in tables, drawings and scanned pages that have no text at all.

What to do with the differences you find

• Check each change against what was agreed: a list of differences makes it hard to miss one.
• Ask about any change you didn't expect before you sign or approve.
• After the other side fixes something, compare again with the new version.
• Keep the final comparison report with the signed document, as a record of what changed in the last round.