AI catches what changes between two versions of any document. Ten minutes now saves you from signing or replying to a document that quietly changed on you.
| Claude PDF limit | Up to 100 pages with visual analysis, 600 pages text only, per Anthropic’s documentation |
|---|---|
| Negation blindness | Vision language models saw about a 25 percent accuracy drop on queries using negation words like “not” or “missing,” per MIT researchers |
| Verification standard | Legal and professional guidance requires a human to independently verify AI output before signing or filing anything based on it |
| Core instruction | “List only changes to numbers, dates, obligations, and names,” then separately check for anything missing from the new version |
1. Get both versions as plain text
Copy the text from the old and new document, or take clear screenshots if it is a scanned PDF. Label them OLD and NEW so the AI does not mix them up. Example: paste your original offer letter as OLD and the revised one as NEW.
2. Ask for meaning changes only, not wording
Tell the AI to ignore rewording, grammar, and formatting, and only list changes to numbers, dates, obligations, and names. This one line does most of the work: ‘Compare these two documents. Ignore wording and formatting changes. List only changes to numbers, dates, obligations, and names.’
3. Force it to check for removals
AI naturally looks for what was added or edited, and quietly misses what was deleted. Add this line every time: ‘Then separately tell me anything that existed in OLD but is missing in NEW.’ This is where the real surprises hide.
4. Ask for a table, not a paragraph
Request the output as: What changed, Old value, New value, Why it matters. A table takes five seconds to scan. A paragraph takes two minutes and you might still miss the one line that matters.
5. Save the exact prompt somewhere you will reuse it
Keep it in your notes app, a pinned chat, or a saved prompt in your AI tool. The value is in doing this every single time a revised document lands in your inbox, not once.
6. Use it on the next revised document you get
Contract, quote, offer letter, policy update, whatever it is. Paste both versions in and run this before you sign or reply, not after.
A worked example
HR sends you a revised offer letter three weeks after your salary negotiation, and it looks basically the same as before.
Before
OLD: Base salary Rs 12,00,000 per year. Notice period 30 days. One time joining bonus Rs 50,000 payable in month one. NEW: Base salary Rs 13,50,000 per year. Notice period 60 days. No joining bonus clause present.
After
Table output from the AI: Base salary changed from 12L to 13.5L, this is the raise you negotiated. Notice period changed from 30 to 60 days, not discussed anywhere, this doubles how long you are locked in if you want to leave later. Joining bonus of Rs 50,000 was removed entirely, not mentioned once in the new letter.
Three ways to bend it
For vendor or procurement contracts
Paste the old and new quote or agreement and ask for changes to price, delivery dates, and penalty clauses. Vendors sometimes tighten penalty terms in a revision while keeping the headline price the same.
For HR policy updates
Compare the old leave policy or benefits document to the new one and ask specifically what benefit was reduced or what new condition was added, since policy rewrites often soften the language around a cut.
For regulatory circulars or notices
If your work involves compliance, paste the old and new version of a circular and ask the AI to list any new obligation or deadline, since these often get added mid paragraph in dense legal language.
When it goes wrong
It listed forty wording changes and buried the one that mattered
Your prompt was not strict enough. Explicitly say ‘ignore rewording, grammar, and formatting, only meaning changing edits’ and repeat it if the first answer still lists trivial changes.
The PDF copy paste came out jumbled and the AI got confused
Some PDFs do not copy cleanly as text. Use an AI tool that can read PDFs directly, or take a screenshot of each page and let it read the image instead of pasted text.
The document is very long and it seems to skip sections
Break it into sections and compare one section at a time, or paste one clause at a time for long contracts. Shorter chunks get read more carefully than one giant block.
When not to use this
This only works when you actually have two versions of the same document. If someone hands you a completely new draft with a different structure, a comparison prompt will confuse more than it clarifies, summarise each one separately instead. And for high value contracts or anything legally binding, treat this as a fast first pass that tells you where to look closely, not a replacement for a lawyer or whoever actually owns that decision. AI can still miss things buried in dense legal language.
What you can now do
You can catch a quietly changed number or clause before you sign or reply, in the time it takes to make tea, instead of reading every line yourself.
Part of Making Life Easier With AI, a weekly walk-through of one small thing AI can take off your plate.
Take this further
Act as a blunt hiring manager who has read ten thousand resumes, not a career coach. I will paste my full resume and the job description I want. Rewrite the whole resume for that role, section by section, in this order: summary, experience, skills, education. Rules: every experience line leads with impact, not duty. Use bracketed placeholders like [8 percent] for any number I did not give you, and list at the end every placeholder I need to replace with a real figure. Keep it to one page of text. Plain formatting only, no tables or columns, so screening software can parse it. After the rewrite, tell me the three weakest claims that need evidence before I send this anywhere. My resume: [paste resume]. The role: [paste job description].
Takeaways
- Save your OLD versus NEW comparison prompt in a notes app or pinned chat so you reuse the exact wording on every revised document instead of retyping it each time.
- Add a standing line asking the AI to list anything present in OLD but missing in NEW, since deletions are what most comparisons quietly skip.
- Ask for output as a table with columns for what changed, old value, new value, and why it matters, instead of accepting a paragraph.
- For long contracts, paste one section or clause at a time rather than the whole document, since shorter chunks get read more carefully.
- Treat the AI’s output as a first pass on anything legally binding or high value, and get a lawyer or the actual document owner to confirm before you sign.
Questions people actually ask
How do I get AI to compare two versions of a contract?
Paste the old version labeled OLD and the new version labeled NEW into the same chat, then ask it to ignore wording and formatting and only list changes to numbers, dates, obligations, and names. Separately ask what existed in OLD but is missing in NEW. Request the result as a table so you can scan it in seconds instead of reading a paragraph.
Why does AI miss things that were deleted from a document?
AI models are generally better at spotting what was added or reworded than at noticing something that simply disappeared, since nothing in the new text points to the missing item. You have to explicitly ask it to check for anything present in the old version but absent from the new one, every single time, or the omission slips through unflagged.
Can AI read a scanned PDF and compare it to another PDF?
Yes, if you use a tool that reads PDFs directly rather than relying on copied and pasted text, which often comes out jumbled from scanned files. Claude, for example, can analyze both text and visual content in PDFs up to about 100 pages. If copy paste looks garbled, screenshot each page instead and let the AI read the images.
Is it safe to rely on AI to catch contract changes before I sign?
It is a fast and useful first pass, not a final check. Legal guidance from firms like Thomson Reuters is clear that anyone relying on AI output for something binding still has to verify it themselves before acting on it. For high value or legally binding documents, use the AI comparison to know where to look closely, then get a lawyer or the document owner to confirm.
What’s the best way to prompt AI for a document comparison table?
Ask for four columns: what changed, old value, new value, and why it matters. Naming the exact columns up front stops the AI from defaulting to a long paragraph that buries the one change that actually matters. Pair it with a strict instruction to ignore rewording and grammar so trivial edits do not crowd out meaningful ones.
Sources
- PDF supportAnthropic
- Study shows vision-language models can’t handle queries with negation wordsMIT News
- If You Can’t Verify It, You Can’t Sign ItThomson Reuters Institute
What happens next
Expect PDF and long document handling in mainstream AI tools to keep improving, which should reduce the copy paste and jumbled scan problems this technique currently has to work around. Watch whether contract and HR software vendors build this kind of before and after comparison directly into their platforms, since that would remove the need for a manual prompt. The requirement for a human to verify anything binding is unlikely to loosen, so this stays a first pass rather than a final check.
