Reviewed practical guide
How to password-protect a PDF and understand its limits
Learn the difference between open and owner passwords, and avoid locking yourself out of your own document.
Protect PDF encrypts the file with 256-bit AES. The main password is required to open the document. An optional owner password controls modification and extraction permissions; when it is left empty, the main password is used for both roles.
Encryption protects a file while stored or sent, but it cannot control what an authorised reader does after opening it. A strong password delivered through a separate channel is more meaningful than relying solely on PDF permissions, which different readers may enforce differently.
What result to expect
You will download “pdf-protegido.pdf”, which should request its password when opened in a compatible PDF reader.