How to Password Protect a PDF (AES 256)
What protection means
When you protect a PDF, its contents are encrypted. Without the password the file is unreadable. 76 PDF uses AES 256, the current standard, through the open source qpdf engine.
Choose a strong password
Use a long phrase of several random words, for example four unrelated words, rather than a short word with a number. Use a password manager so you do not forget it. A forgotten password cannot be recovered.
Share the password separately
Do not put the password in the same email as the file. Send it by a different channel, such as a text message or a phone call.
Printing and copying
You can ask viewers to block printing and copying. Most PDF viewers respect these settings, but they are not as strong as the open password, so treat them as a courtesy.
Everything stays on your device
Both the file and the password are handled in your browser. Nothing is uploaded.