Banks and insurers often send statements locked with a password. If you know the password and the document is yours, you can save an unlocked copy and stop retyping it.
There is no way to remove a password you do not have. Encryption is the point of the feature, and a tool that could bypass it would make every protected document on the internet worthless. If you have lost the password, the only route is whoever issued the file.
For bank statements the password is usually derived from something you know, often a date of birth or part of an account or card number, and the covering email normally spells out the formula.
Think about where the unlocked copy ends up. A statement with the password removed is readable by anyone who can see the file, so keep it somewhere sensible rather than a shared downloads folder.
The unlocked file is a new document with the pages copied into it, saved with the name of the original and the word unlocked added. Your protected original is left exactly as it was, so nothing is lost if you want to keep it.
If the file will go somewhere shared, think about whether it should have a password at all. If it should, you can add a fresh one of your own with the same tool. A long phrase kept in a password manager is better than a short word you will have to remember.
No. You need the password to unlock the document, here or anywhere else.
No. It is unlocked by your own browser, which matters rather a lot for a bank statement.
Yes, the same tool does both. Nobody can recover it for you, so write it down somewhere safe.
Check for caps lock and for a trailing space, and make sure it is the password to open the document. The tool cannot get around a password it does not have, so a wrong one always fails.