How to password protect a PDF

With an open password and a modern encryption revision, a PDF reader cannot recover the page content without deriving the correct key. This is the mechanism to evaluate when confidentiality at rest or in transit matters.

Permission flags are entries in the encryption dictionary that ask a compliant viewer to withhold actions such as printing or copying. A viewer can ignore them, and anything that can render the page can usually reproduce its content. Treat flags as signalling, not access control.

A strong cipher does not rescue a guessable password. Store the password separately from the file and use external encryption software whose supported revisions, key handling and recovery process you understand.

PDF Encryption Checker reads the encryption dictionary and reports what the file declares, such as a cipher or revision. It is an inspector, not a proof that the implementation is correct, the password is strong or the document is safe against every threat.

PDF Permissions Checker reports permission bits. Its report cannot make those bits enforceable, and a compliant-looking result is not a guarantee that every viewer or extraction path will cooperate.

PDF Security Inspector and metadata tools can expose declared properties or ordinary metadata. They do not encrypt, decrypt, recover forgotten passwords or certify compliance.

Rewriting, decrypting or re-encrypting a PDF may invalidate an existing digital signature and can change metadata, page structures or other evidence. Preserve the original protected file before using external software to make a working copy.

If you have forgotten an open password, do not expect an honest tool to bypass it. Use the authorised recovery or records process for the document owner. A checker can describe protection that is already present; it cannot recover access.