There might be two different reasons why "sign pro PDF" ask you to enter a password.
- It’s possible that the PDF document was encrypted with an owner password, preventing you from gaining access. You will need to enter the valid owner password in order to open the document.
The message shown from "sign pro PDF" is referring to 'document's password' and looks like:
To get the password for such a document you need to get in contact with the person who created the document. - It is possible that a password was entered while the 'Personal Digital Certificate' was created and the fields marked in green was filled:
The message shown from "sign pro PDF" is referring to 'password for the default certificate'
If you don't want to enter a password you would need to delete the 'Personal Digital Certificate', because a saved certificate cannot be edited afterwards. Create a new 'Personal Digital Certificate' and leave the optional Password & Confirmation fields empty.
If it is not a 'Personal Digital Certificate' but a certificate that was provided by a 3rd party provider, you would need to contact them.