In the context of PDF files, the terms "Owner Password" and "User Password" often appear.

The user password has to be entered already to read an encrypted document. With the user password, it is not possible to change or reset the security settings when saving. In addition to the protection against unauthorized opening, additional usage restrictions can be set. These include: Printing not allowed, document modification not allowed, etc.

The owner password allows to change the user password or the permissions. If the owner password is already specified when opening a file protected by the user and owner passwords, the usage restrictions set by the permissions do not apply.

The CIB pdf toolbox requires passwords to be set for various functions. It is also possible to set new passwords for the target file when editing PDF files.

The following questions and answers will hopefully help:

1. Can a PDF have an owner password and no user password?
   Yes, this is the case if the user can read the PDF but not edit it (or save/print/whatever is set).
2. Can a PDF have a user password and no owner password?
   No, in this case the owner password is automatically set internally to the same value as the user password.
3. Which of the two passwords is required to open the file in the reader at all?
   To open the PDF in a reader, either the owner password or the user password can be entered.
4. A PDF cannot be encrypted at the same time and have both passwords blank. If both passwords are empty, the PDF will always be saved unencrypted.