Nothing starts until you press the button.
Passwords
Everyone who opens this file has to type it. A lost password cannot be recovered here or anywhere else, and this one never leaves your device.
Type it twice. A password with a typo in it locks the file just as well, and cannot be recovered.
Optional, and different from the one above. It lets you change the permissions later without unlocking the file for everyone who reads it.
Set a password to open the file, a password to change permissions, or both. With neither, protecting the file changes nothing about it.
Encryption
What readers may do
Permissions are a request, not a lock. Software that follows the standard honours them; software that ignores them can still print and copy. Only the password to open decides who reads the file.
Permissions