PDFs carry two kinds of password, and the one you are hitting was set by whoever produced the file — a bank, a payroll system, a government portal. If it asks before showing anything, you need that password. If it opens but blocks printing, no password is needed to clear it.
1Check the covering email or letterEncrypted statements almost always come with a line explaining the password format. It is the most common answer and takes ten seconds to find.
2Try the obvious valuesDate of birth in the formats DDMMYYYY and YYYYMMDD, postcode without a space, the last four or six digits of an account or policy number, customer reference.
3If it opens, save a copy without the passwordRemove PDF Password decrypts it in your browser once you type the password, so you never type it again. Nothing is uploaded, including the password.
4If nobody has the password, ask for a new copyThere is no legitimate way around an open password, and any site offering to remove one without it is either failing or lying.
Why does this happen?
The sender encrypted it automatically. Banks, insurers and payroll systems encrypt statements as a matter of policy, usually with your date of birth, postcode or the last digits of an account number.
A document system applied a policy. Corporate document management and e-filing systems often add protection on export, without telling the person who exported the file.
It is a permissions password, not an open password. If the file opens and only printing or copying is blocked, nobody needs to know a password: the restriction is a flag inside a readable file.
It was made from a template that carried protection. Protection set in an original spreadsheet or document can survive export, so a file nobody deliberately locked arrives locked.
Questions
Can you remove a PDF password without knowing it?
No. A file protected with an open password is encrypted; without the password there is nothing readable to save. Tools that promise otherwise are selling brute force, and it rarely works.
My reader opens it but Acrobat asks for a password. Why?
Different readers treat permission flags differently. A file with an owner password opens anywhere; Acrobat may still prompt before letting you edit it.
Is typing the password into a web page safe?
Here it is used only inside your browser tab — there is no server to send it to. On a site that uploads your file, you are handing over both the document and its password.