How to Password Protect a PDF (Full Walkthrough)
Real PDF password protection encrypts the document's contents so it can't be opened without the password — this requires cryptographic support that this site's Encrypt PDF tool doesn't have yet (the pinned PDF library it's built on can't write real encryption, and it honestly refuses rather than producing a file that looks protected but isn't). Until that's added, the reliable free options are your OS's built-in tools: on Mac, Preview can add a password via File > Export, and on Windows, Microsoft Print to PDF combined with Word's "Encrypt with Password" (File > Info > Protect Document) both use real encryption.
Why this matters more than it sounds
A PDF tool that fakes password protection — accepting a password, showing a success message, but producing a file anyone can still open — is worse than no protection at all, because it gives false confidence. That's why this site's Encrypt PDF tool refuses the operation outright instead of faking it, and explains why on its own page.
Where to actually password-protect a PDF today
On a Mac: open the PDF in Preview, choose File > Export, check "Encrypt," and set a password.
On Windows: if the document originated in Word, use File > Info > Protect Document > Encrypt with Password before exporting to PDF. Adobe Acrobat (paid) can also add password protection to an existing PDF directly.
Whichever method you use, store the password somewhere safe — losing it on a genuinely encrypted PDF means the document becomes permanently inaccessible, which is the intended behavior of real encryption.