You can also muck with associations at the command prompt. The two key commands are
On my PC I see the following
Code:
assoc .acsm
.acsm=Adobe.ACSMessage
ftype Adobe.ACSMessage
Adobe.ACSMessage="C:\Program Files (x86)\Adobe\Adobe Digital Editions\digitaleditions.exe" "%1"
ftype shows the linkage from a file type to an file type association
assoc then shows the linkage from an association to a program