Adobe PDF security: is it really just an "honor code"?

When encrypting a PDF in Adobe Acrobat Pro XI, there's a message to the effect that some third-party programs which read PDFs may ignore the encryption password and open the PDF for viewing. Is Adobe PDF encryption really no more than a sign on a door that reads

This door is locked. The key is in the lock. But don't use it.

??

All Adobe products enforce the restrictions set by the Permissions Password. However, not all third-party products fully support and respect these settings. Recipients using such third-party products might be able to bypass some of the restrictions you have set.

Solution 1:

If you add a password to view a PDF, then the file is actually encrypted. There is no "honor system" - any program will have to have the password, or somehow crack the security, to view the file and edit it in any way.

If you add a password to control any other functions, such as printing or editing, then the "honor system" is in effect - while Adobe products and most other big-name PDF readers will honor these restrictions, there is nothing preventing a program from just ignoring them, and nothing preventing the user from simply opening the PDF in a text editor and removing the "restrictions". Hence, the reference in the message to a "permissions password".