How to anonymize a PDF or Word document before using ChatGPT

Step 1: work from a copy, not the original

Never edit the only copy of a client document. Make a working copy, and keep the original somewhere ChatGPT never sees. If the document is a scan, you need its text first, which means OCR, and OCR mistakes can hide names from simple search.

Step 2: replace details consistently

Replace people, organisations, addresses, emails, phone numbers, dates of birth and ID numbers with typed placeholders. Consistency matters more than style: the same person must get the same placeholder every time, or ChatGPT will treat them as different people and its answer will be wrong.

Keep a private key, such as [PERSON_001] = the client, stored with the original and never pasted into the chat.

Step 3: review the whole copy

Read the entire redacted copy, not just the highlighted changes. Look at headers, footers, signatures, tables and file names, where details often survive. The Law Society of Ontario’s white paper warns that even anonymized facts can sometimes be pieced back together, so remove unusual identifying facts too.

Step 4: share only the reviewed copy, then restore

Paste the reviewed text or upload the reviewed file. Ask ChatGPT to keep the placeholders exactly as written. When the answer comes back, replace each placeholder with the real detail using your private key, and check any placeholder ChatGPT changed, merged or dropped.

Remember that the AI provider still processes what you share. Replacing identifiers reduces what it receives; it does not change the provider’s terms.

Anonymized or pseudonymized: why the word matters

A copy is anonymous only if nobody can link it back to the person. A copy with tokens and a private key is pseudonymized: you can reverse it, which is the point, because you want the real names back in the finished document. Privacy regulators in Canada, the EU and the UK treat pseudonymized text as personal information in the hands of whoever holds the key.

What changes is who can read the identities. ChatGPT receives the facts with the names and numbers swapped out and has no way to reverse the tokens. The key stays with you. That is a real reduction in what you disclose, but your confidentiality and consent obligations still apply to the copy.