What does it mean to unlock a PDF?
A password-protected PDF can require a password before its contents can be opened. If you know that password, you can use a PDF unlocker to create a copy without the original password protection.
This can be useful when you regularly work with documents that require a password but need an easier-to-open copy for your own workflow.
The original file is not replaced. The result is generated as a separate PDF so you can keep your original protected document.