Can this remove a password I do not know?
No. Removing an open password requires opening the file, which requires the password. This is for decks you are entitled to open, not for recovering lost passwords.
What can be removed without a password?
Write protection and the marked-as-final flag, because they are settings inside a file that is already readable — unlike an open password, which encrypts it.
Which formats can protection be removed from?
PPT, PPTX and ODP — the same formats that can carry it. Removing it is simply saving the presentation again with the protection settings cleared.
How do I confirm the protection is really gone?
Save the file and open it again without supplying a password. If it opens, the open password is gone; checking the protection properties on the in-memory object is not the same test.
