It sounds as if ADE doesn't know how to parse a filename correctly (along with many other things it can't do correctly).
Renaming your xxx.pdf.acsm file to xxx.acsm (or_anything_else_without_a_dot.acsm) and trying again.
Thanks for the reply. The problem was that only the Adobe Digital Editions can open acsm, and the file was going to the Adobe Reader instead. Why that isn't changed when you download the book reader I cannot imagine.