Two kinds of PDF protection
An open password stops a PDF from opening at all. Banks, payroll systems and phone companies often use one on statements, typically based on your date of birth or account number. Enter it here once and you get a copy you can open, merge or compress without typing it every time.
A permissions password lets anyone open the PDF but blocks printing, copying or editing. These restrictions can be removed without knowing the password: leave the box empty and tap Unlock.
This is not a password cracker
If you don't know the open password, this tool can't unlock the file, and it does not try to guess it. Only unlock documents that you own or have permission to change.
Unlocking happens entirely on your device using the open-source qpdf engine, so your PDF and password are never uploaded.