Password Protected PDF Files in Elementary OS

I have installed Acrobat 9.5.5 on my Elementary OS (Ubuntu base) system but when I try to open a password protected PDF file from my bank Acrobat fails with the error "There was an error opening this document. An updated version of Acrobat is needed in order to open this document.".

The version that I have installed claims to be 9.5.5 04/26/2013.

Has anyone got any pointers?

Thanks