# How to compare two documents with AI and check the changes

Before comparing documents with AI, confirm which versions you have and what kind of difference matters. Keep each difference tied to a page, section, or paragraph. A summary that blends both documents can conceal the exact change you need to review.

## Inventory the inputs
Record filenames, dates, page counts, and whether the text is selectable or scanned. Give documents neutral labels such as A and B. Do not assume the file with “final” in its name is the approved version. If text extraction is incomplete, resolve that before treating an absence as a deletion.

## A fictional change table
| Location | Document A | Document B | Review question |
| --- | --- | --- | --- |
| Delivery section | Ten business days | Fifteen business days | Was the schedule change approved? |
| Appendix | Two revision rounds | Not found in extracted text | Is the appendix missing or unreadable? |

“Not found” requires a source check. It is not yet proof that the term was removed. Tables, footnotes, and scanned pages are especially worth inspecting visually.

## Give the model a comparison brief
```text
Compare documents A and B for changes in obligations, amounts, dates,
exceptions, and scope.
Quote the relevant wording from both and include exact locations.
Keep a separate list of extraction gaps and unreadable sections.
Do not merge the versions into one text or interpret legal enforceability.
Document inventory: [filenames, dates, labels]
Texts with locations: [paste]
```

## Review the important differences yourself
Open the original pages behind changes to deadlines, prices, obligations, and exclusions. A model may paraphrase away a condition that determines the meaning. Keep exact wording in the comparison record when it matters.

Use AI’s table to prepare questions for the document owner or a qualified adviser. It can organize a comparison, but it does not certify that every difference was found or provide a legal interpretation. Save the original files and the comparison separately so someone reviewing the decision can trace each point back to the right version.

## Work through one change before comparing the whole file
Here is a fictional pair of passages:

Document A, section 3: “The first draft is due within ten business days after the client supplies the approved photographs. Two revision rounds are included.”

Document B, section 3: “The first draft is due within fifteen business days after the client supplies the approved photographs. Two revision rounds are included, provided feedback is returned within five business days.”

A useful comparison records both the longer delivery period and the new condition on revisions. “Delivery changed from ten to fifteen days” misses the word “business” and the starting event. “Two revision rounds are still included” misses the added condition.

| Change | A | B | What to confirm |
| --- | --- | --- | --- |
| First-draft period | Ten business days | Fifteen business days | Was the revised period agreed? |
| Start of period | Approved photographs supplied | Same wording | Which record confirms receipt? |
| Revision condition | No condition in this passage | Feedback within five business days | Who should clarify how the condition applies? |

The table describes the text. It does not decide which version controls or what a legal consequence would be.

## Compare long documents in sections
Keep headings and page labels when preparing the text. Compare corresponding sections first, then review the table of contents, appendices, and cross-references. Ask for a list of sections examined so you can see whether part of a document was skipped. If your AI app cannot hold both documents at once, work in named sections rather than asking it to remember a large earlier upload indefinitely.

After a section comparison, save the findings with the original filenames. At the end, combine the findings into one change list while retaining their locations. Inspect repeated amounts and dates: the same term may appear in a main section and an appendix, and those places may have changed differently.

## What if one document is scanned?
Check a sample of extracted text against the image first. A misread digit can look like a price change; a missing table can look like a deleted requirement. If the app cannot read a page, mark it as unreadable and review it separately. Do not ask it to fill the gap from surrounding text.

For a quick summary, you can request the most important changes first, but keep the complete change table. A short answer helps you prioritize review; it does not establish that the comparison is complete.

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SkillStall · 2026-10-03