How to compare confidential documents without uploading them

Updated 1 October 2026

Online comparison tools are convenient, but most of them work by uploading both files to the provider's server. For a draft contract, a batch record, a patient-facing document or an unreleased SOP, that may break your company's data handling rules before you have even seen the result.

Why uploading is a problem

• You lose control of the copy. Once a file is on someone else's server, you rely on their retention, logging and access controls.
• It may need approval. Many companies require a supplier assessment before confidential data goes to a new service. Few people do that for a quick compare.
• Regulated content raises the stakes. Quality records, clinical documents and personal data often come with contractual or legal limits on where they can be stored.

Three safe options

1. Word's own Compare. In Word, go to Review → Compare → Compare, choose the original and revised files, and Word builds a compared document on your computer. It is thorough, but the output can be hard to read when there are many changes.
2. A desktop comparison tool approved by your IT team. These work offline but usually need installing and a licence per seat.
3. A browser-based tool that does not upload. Modern browsers can open and process a .docx entirely on your device. The page is downloaded once, then the comparison runs locally and the files never leave your computer.

How to check a tool really keeps files local

Don't take the marketing at its word. You can check it yourself in a couple of minutes:

1. Open the tool, then open your browser's developer tools (F12, or Cmd+Option+I on a Mac) and choose the Network tab.
2. Load two documents and run the comparison.
3. Watch the list of requests. If your file is uploaded, you will see a large request go out as you add it. A tool that works locally shows no new requests carrying your data.
4. For extra confidence, load the page, then switch off Wi-Fi and try again. A local tool keeps working.

RevisionProof is built this way. The compare page sets a strict browser security policy that stops it connecting to any server, so even a bug could not upload your files. You can confirm it with the steps above.

Keep a record

If the comparison is part of a review or approval, save the result with something that identifies exactly which files were compared. RevisionProof's change report includes a SHA-256 fingerprint of each file, so anyone can later confirm the report matches the documents on file.