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Comparing two versions of a contract

A contract goes out, comes back, and nobody says what moved. Word can compare documents. PDF cannot — and contracts arrive as PDF.

Why this is hard at all

Word has Compare Documents, and it is good: it knows the document structure, so it can tell you a clause moved rather than claiming it was deleted and a new one added. PDF has none of that. A PDF was chosen precisely so the document could not be edited, and the same property that protects it also strips out everything a comparison tool would use.

So comparing PDFs means reconstructing text from positions, then comparing the text. Which works — but the reconstruction step introduces failures that have nothing to do with the contract.

The change that matters is usually one word

In practice the dangerous edits are small and dull:

A payment term moves from thirty (30) days to forty-five (45) days.
A figure changes: 4,200 becomes 4,650.
A notice period doubles.
One sentence is deleted — often the one that protected you.
A currency symbol changes and nothing else does.

None of these change the shape of the document. Scrolled past at speed, they are invisible. That is why a comparison has to mark the word, not just the paragraph.

The failure to watch for. Some comparison tools normalise text before comparing — they strip punctuation and symbols to avoid noise. A tool that does that will tell you $500 and €500 are the same line, and that 5% per annum is unchanged when it now reads 5 per annum. In a comparison tool, failing silently means reporting "nothing changed" — which is exactly the answer that gets a document signed unread.

Reformatting looks like a change, and is not

If the second version was re-exported with different margins or a different font size, lines break in different places. A line-by-line comparison will mark paragraphs as changed when not a single word moved. This is the most common source of noise, and the reason the marks should be at word level: a reformatted paragraph with no word changes shows as a paragraph with no marks inside it.

A checklist that catches what tools miss

Numbers first. Read every figure in both versions: amounts, percentages, day counts, dates. They are where the money is.
Count the clauses. If version two has one fewer, something was removed — find it before anything else.
Check the defined terms. A change to what "Services" means can rewrite the whole agreement without touching another word.
Check signature blocks and annexes. They are pasted, moved and forgotten more than any other part.
Never accept "no changes" from a tool without a spot check. Open both at one clause you know was discussed. If the tool says it is identical and it is not, stop trusting the tool.

If the contract is a scan

A signed contract is often scanned, and a scan has no text. There is nothing to compare, and a tool that reports "no differences" on two scans is telling you nothing at all — the only honest answer is that it cannot read them.

Redline → Drop the two versions, see them side by side with every changed word marked. Neither file leaves your browser. Free to use.