The Passwords preferences are used to create a database of stored passwords that is used when PDF-Tools is processing files:
Figure 1. Preferences Dialog Box, Passwords Tab
If processed files are password-protected and the relevant password is included in this list then PDF-Tools will not prompt for a password.
•Click Add to add new passwords to the list.
•Click Edit to edit the name of existing passwords.
•Click Remove to remove selected passwords.
•Click Clear to remove all passwords from the list.
Click OK to save changes.