Add a password to a PDF with strong AES-256 encryption, and optionally block printing or copying.
Need a strong password? Use the password generator. To remove a password later, use Unlock PDF.
The PDF is encrypted with AES-256, the strongest standard encryption for PDFs. Without the password, the content can't be read. Use a long password (12 characters or more) that you don't use anywhere else.
They control what people can do after opening the file, such as printing or copying text. Most PDF apps respect them, but they're easier to bypass than the open password, so don't rely on them for secrets.
There is no way to recover it, so the file can't be opened. Keep your original unprotected copy, or store the password in a password manager.
AES-256 is supported by Adobe Acrobat Reader, Preview on Mac, iPhone and Android, Chrome, Edge and Firefox. Very old PDF readers (from before about 2010) may not open it.