A PDF carries more than the pages you can see. Author names, software fingerprints, revision timestamps, cropped-away image regions and text hidden underneath graphics all travel with the file, and several well-documented public leaks have come from exactly this.
These guides cover what is hidden inside a typical PDF, the difference between covering information and removing it, and a practical pre-send checklist for documents that matter.
A PDF carries author names, software fingerprints, timestamps, and sometimes earlier versions of its own content — none of it visible when you read the pages.
Drawing a black rectangle hides text from your eyes while leaving it fully recoverable in the file — real redaction has to remove the underlying content.
A drawn signature is a picture on a page — fine for everyday consent, but it proves nothing cryptographically about who signed or whether the document changed.
Five checks, in order, that catch the overwhelming majority of accidental disclosures — each takes under a minute.