Encrypted PDF file cannot be edited
If the recipient states that they can open the file but cannot fill in fields or make changes to the file, provide the correct password for the file.
Find out what password the customer used to open the file. If they used the User password, they have read-only permission to the file. You must provide the Owner password to permit editing the file, including filling in forms.
If they did not use a password to open the file, but need one to do additional tasks, provide the Owner password.