How to Compare Documents and Extract Differences with AI

Do not ask a model, “What changed?” and trust that absence means no difference. Extract text deterministically, preserve a conventional diff, and use AI to organize the evidence.

Workflow

1. Confirm both files are the intended versions and retain immutable originals.
2. OCR scans, then verify headings, tables, footnotes, and page numbers.
3. Create a structural or text diff outside the model. Give Claude, ChatGPT, Gemini, or Microsoft Copilot the diff plus both documents.
4. Ask for a table: section, old language, new language, change type, likely impact, page references, and confidence.
5. Review all deletions, numbers, dates, obligations, definitions, exceptions, and appendix changes manually.

Controls

Define materiality before comparison. A legal reviewer, not the model, decides legal effect. Keep confidential files inside an approved product and plan. Require the assistant to say “not found” rather than fill a gap.

The deliverable should link every summary claim to exact source language. If a reviewer cannot reproduce it, it is commentary, not evidence.

Sources & further reading

• Claude product
• ChatGPT product