Im trying to password protect a pdf, I have Adobe XI, supposed to get a drop down when I hit the tools on the tool bar and there is no dropdown, can't get there from properties either (saw this on an Adobe video). Help?

I have Adobe XI. Trying to figure out how to password protect a document. Neither the properties tab nor tools tabs give me a drop down to password protect. The properties tab security says, this document's security method restricts what can be done to the document. Then it says "no security" under the security method. How do I do this?