Remove hidden information from a PDF before you share it

A PDF often carries more than what you see on the page. Before you send a document to a client, post it publicly or file it, it's worth checking for four kinds of hidden information.

1. Document properties (metadata)

Most apps write the author's name, the software used and creation and edit dates into the file. A report written on a colleague's laptop can carry their name; a "new" document can reveal it's a reused template from three years ago.

Check: in most PDF readers, File, then Properties. Fix: Remove PDF Metadata deletes these fields, including the XMP copy many apps also store.

2. Comments and markup

Review comments, sticky notes and highlights stay in the file even when they're hidden by your viewer's settings. Internal remarks like "check this figure with legal" have a way of reaching the wrong people.

Fix: delete comments you don't want to send, then run Flatten PDF to burn any remaining markup into the page so it can't be edited.

3. Form data

A filled-in form keeps its answers as editable fields. Anyone can change them, and some apps keep values in fields you can't see. Flattening turns the answers into fixed page content.

4. Things that look removed but aren't

This is the one that causes real leaks. Drawing a black box over text in a PDF editor hides it but doesn't remove it: the text is still there, underneath, and can be copied out. Real redaction removes the content itself, or turns the page into an image so the original text is gone.

Check: after redacting, try selecting the hidden area and pasting it into a text editor. If text appears, it wasn't redacted.

A quick checklist

1. Delete comments you don't want to share.
2. Flatten forms and markup.
3. Redact properly, and test it by copying.
4. Remove the metadata last, since other tools may add their own.

All of the tools linked here run in your browser, so the document never leaves your device.