Compare two documents by identifying versions, aligning corresponding sections, classifying additions, removals, and meaning changes, and attaching evidence from both files. Use deterministic diff tools for exact text and AI for interpretation. A qualified reviewer should verify consequential legal, financial, or safety changes.
Who this is for: Reviewers comparing contracts, policies, proposals, reports, or revisions where wording changes can affect decisions.
- Confirm document identity and version order before interpreting any difference.
- Combine exact text comparison with semantic review because each catches different changes.
- Require old and new evidence locations for every material change in the report.
Establish the comparison basis
Record file names, titles, dates, authors, approval states, and which version is considered earlier. Check whether one file is a clean copy and the other contains tracked changes. Do not compare documents that cover different jurisdictions, products, or periods without stating that difference explicitly.
Define materiality for the task. A legal reviewer may care about obligation, permission, deadline, liability, and defined-term changes. An editor may focus on argument and evidence. A product team may track requirements and acceptance criteria. The comparison prompt should reflect that purpose rather than merely list every wording change.
Align corresponding content
Map headings and sections even when numbering moved. Use exact diff software to find insertions and deletions, then group related edits into logical changes. If a section was split or relocated, record the mapping. Similar paragraph order does not prove that the documents share the same structure.
Preserve document and page identifiers in extracted text. Tables need row and column alignment, not paragraph comparison. Definitions deserve special attention because one changed definition can alter many unchanged clauses. Ask the model to mark content with no clear counterpart instead of forcing an alignment.
Classify meaning changes
Useful categories include added requirement, removed requirement, narrowed scope, expanded scope, changed actor, changed timing, changed number, clarification, and editorial-only change. Require a short explanation of practical effect with quoted old and new wording. The explanation should not exceed what the text establishes.
Negation, modality, and qualifiers are high risk. Replacing may with must changes obligation; changing within 30 days to after 30 days reverses timing. A model can miss small tokens while describing broad themes well. Add targeted checks for names, dates, amounts, percentages, units, defined terms, and words such as not or except.
Verify and communicate impact
Review every high-impact row against both original documents. Separate textual change from business or legal interpretation. The comparison can say that a deadline changed from one date to another; whether that creates breach risk may require counsel or an accountable owner. Include unresolved mappings and extraction problems in the report.
Present changes by materiality and topic, with a full appendix if exhaustive coverage is required. Keep exact-diff output available. If documents are long, test known changes and known unchanged passages before trusting the workflow. Re-run after model, parser, or document-format changes.
Compare two vendor policy versions
A company receives a revised data-processing policy and needs to identify operational changes before renewal.
- Verify both policy dates, approval status, and that they cover the same service and jurisdiction.
- Run an exact diff and build a heading map for renamed or moved sections.
- Ask for material changes in retention, subprocessors, incident notice, audit rights, and customer duties with old and new quotations.
- Run separate checks for every duration, deadline, named party, and exception.
- Have privacy and contract owners verify the cited clauses and determine operational impact.
Material change register
Create one row for each logical change rather than every changed word.
- Version identity: old file, new file, dates, scope, approval state, and comparison direction.
- Alignment: old section and location, new section and location, plus mapping confidence.
- Change class: addition, removal, scope, actor, timing, number, definition, exception, or editorial.
- Evidence: exact old wording, exact new wording, and concise text-grounded effect.
- Disposition: owner, required action, specialist review, unresolved question, and completion status.
Common mistakes
- Asking only for a thematic summary and missing a one-word change to an obligation.
- Letting the model align unrelated sections because their headings sound similar.
- Reporting legal or financial impact as settled without accountable specialist review.
Try one
Version A says a supplier 'may notify within 72 hours'; Version B says it 'must notify within 48 hours.' How should the comparison record this?
The register should quote both clauses, classify changes to obligation and timing, cite both locations, and state that the wording becomes mandatory and the stated window shortens. A strong answer flags operational or legal impact for responsible review rather than declaring a legal conclusion. Evaluation should catch both may-to-must and 72-to-48 changes.
Sources
- Gemini API long context guideOfficial guidance for reasoning over large inputs and locating relevant material.
- Gemini API document processing guideOfficial guidance for understanding PDF documents and their visual elements.