Add Text does not work

I upgraded my computers in December of 2014.  I purchased new Adobe Acrobat XI licenses at the same time.  I have version 11.0.16.  Now, when I try to add text to a pdf document (Edit, Edit Text & Images, or Tools, Content Editing, Add Text), I get a message that says:

This form cannot be edited in Acrobat.  Please use Adobe LiveCycle Designer to edit this form.

My older versions of Acrobat used to allow me to add text to pdf documents.  Can someone tell me why the newer version no longer has that functionality?  

If Adobe will not permit me to add text to pdf documents, why is the option to do this in the program?  Am I missing something here? 

Thanks.