How to Unlock a Password-Protected PDF File
"Unlocking" a PDF usually means one of two different things: removing print/copy/edit restrictions from a file whose permissions you're authorized to change, or recovering access to a file whose password you don't know. This site's Unlock PDF tool can read and explain a PDF's permission flags, but honestly cannot currently strip real password encryption — the pinned PDF library it uses cannot write or remove genuine encryption. If you know the password, your PDF viewer's own "remove security" feature (available in Adobe Acrobat and some other viewers) is the reliable option today; if you don't know the password, no legitimate free tool can bypass real encryption, and you should contact whoever issued the document.
Open the Unlock PDF Permissions tool
Two very different problems that both get called "unlocking"
A permissions-restricted PDF (no password needed to open, but printing/copying/editing is disabled) is a different problem from a password-protected PDF (a password is required just to open it). The first can sometimes be addressed with the file's original creator or the software that made it; the second requires the actual password — there is no legitimate way around real PDF encryption without it.
What this site's Unlock PDF tool actually does right now
It reads the PDF's permission bits (a real, standards-based feature of the PDF format) and gives you an accurate explanation of what's restricted and why — but it does not attempt to strip real encryption, because the underlying PDF library this build uses cannot do that safely. Rather than pretend to succeed and hand you back a file that looks unlocked but isn't, it tells you honestly what it can't do yet.
What to do today
If you're authorized to remove protection and know the password: Adobe Acrobat's "Remove Security" feature, or your document's original creation software, is the most reliable path right now. If you don't know the password: there is no ethical shortcut — password-protected PDFs from banks, government agencies, and employers exist specifically to restrict access, and legitimate use means contacting the issuer for the password or a re-issued copy.