Error message when trying to open downloaded e-book as PDF

I downloaded an e-book that I need to view as a PDF. I found the PDF files of the book in the "my digital editions" folder in my documents but when I try to open them I get an error message saying "There was an error opening this document. The security plug-in required by this command is unavailable". I have already authorized my digital editions program with my adobe ID. Any help would be great.

Thanks.