BASALT · JOURNAL
How to compare two contract PDFs on a Mac
PDF comparison can mean pixel difference or text difference. For contract review, text-level comparison is usually more useful: a font substitution should not bury a changed indemnity clause under thousands of visual differences.
Prepare comparable text
Confirm that both files represent the intended versions and record their hashes. If either is scanned, OCR it first and spot-check the text. Differences caused by OCR errors should be classified separately from drafting changes.
Remove recurring page furniture such as Bates stamps or confidentiality watermarks from the comparison view when the tool supports it, but do not modify the source files. Normalize soft hyphens and line-wrap artifacts so re-pagination does not appear as rewritten prose.
Compare meaning in context
Review insertions, deletions, and moved passages with surrounding clause numbers. Pay special attention to defined terms, negation, dates, monetary thresholds, cross-references, and exhibit references. A one-character change can matter more than a rewritten paragraph.
Tables need visual confirmation because extracted reading order can interleave columns. Signature pages and handwritten edits are images and require separate comparison.
Export and verify the blackline
A blackline is a review aid, not a replacement for either source. Label the base and revised versions, include their hashes, and link each change to source page or clause. Open the exported comparison and confirm that additions and deletions are not clipped or misordered.
If either contract contains confidential material, sanitize the blackline too; comparison output may quote text from both versions and inherit metadata.
Frequently asked questions
Is visual PDF comparison best for contracts?
Usually not. Small layout shifts create noise. Text-level comparison better isolates drafting changes, with visual review for tables, images, and signatures.
Can I compare a scan with a digital PDF?
Yes after OCR, but classify likely recognition errors and verify important changes against the page images.
Does a blackline replace the source versions?
No. Preserve both originals and treat the blackline as a derived review artifact.
Doing it in Basalt
Basalt performs text-level document comparison and exports a blackline, deliberately avoiding hairline layout noise. OCR runs locally for scans, and every source remains unchanged. Get Basalt.
Redaction that proves itself
Basalt destroys the content you mark, then re-opens the file it wrote and proves the content is gone before it saves anything. Your documents never leave your Mac.