Can I redline a scanned PDF (image, no text layer)?

Not directly. You need to generate a text layer first via OCR. Run the scanned PDF through our PDF OCR tool — which adds a searchable text layer in-browser — then use the OCR'd version as your input to the redline tool. Be aware that OCR errors can introduce spurious differences, so review the OCR output for accuracy before comparing.

Will the redline detect formatting changes (bold, fonts, margins)?

No. Text-based redlining compares the text content only, not the visual formatting. This is usually what you want for contract review — the legal substance is in the words, not the typography. If formatting changes matter (a contract specifies particular visual layout, or you're reviewing a document where formatting carries meaning), pair the text redline with a visual side-by-side comparison in a PDF reader.

Is my contract uploaded anywhere?

No. All file parsing and diff computation happens entirely in your browser. pdf.js handles PDF text extraction client-side, mammoth handles DOCX, the diff runs in JavaScript — nothing is transmitted to any server. This makes the tool appropriate even for highly sensitive commercial contracts where uploading to a third-party service would be a security violation.

How large can my contracts be?

In practice, the tool handles typical commercial contracts (up to about 50,000 words per file) comfortably on modern devices. Very long contracts (200+ pages, like some M&A agreements or financing documents) may hit browser memory limits; the tool will warn you if the comparison is too large and suggest using line-level granularity instead of word-level, which is substantially faster.

Should I use word-level or line-level diff?

Default to word-level for standard contract review — it catches subtle wording changes (a 'reasonable' swapped for 'best,' a 'shall' swapped for 'may') that line-level misses. Switch to line-level for large documents with lots of structural changes where word-level becomes noisy, or when you're scanning for 'what sections changed' rather than 'what words changed.'

Can I use this for non-contract documents?

Yes. The tool works on any text-bearing PDF, DOCX, TXT, or MD file. It's branded for contract work because that's the highest-stakes use case, but it works equally well for comparing policy documents, research papers, code documentation, meeting minutes — anything where you need to know what changed between two versions.

How to Redline a Contract (2026)

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