A PDF can look safely redacted while still containing the original email address, phone number, or identifier in its text layer.
That happens when someone draws a black rectangle over text instead of creating a copy where the content is no longer present. The visual result may look identical, but the risk is not: the covered text can sometimes still be selected, copied, searched, or extracted.
This post documents a small reproducible test using only synthetic values. It is not a claim that automatic detection makes every PDF safe. It is a checklist for deciding whether a downloaded file has actually stopped exposing the markers you intended to remove.
The test file
The three-page sample contains deliberately fake markers:
