How to [really] password protect a PDF?

What is the use of password protection when there are free websites (i.e. pdfunlock.com) on the internet that can remove password protection from a PDF file to gain full read write access? Autodesk has just implemented complete reverse engineering of PDF files back into AutoCAD.

What happened to copyright and proprietary rights and why is it so easy to crack these passwords. Hopefully people realize that password protection of a PDF is far from safe.