Well, that changes things (only a bit, see below), but then again, even if they had a linux client it wouldn't help you.
WINE
should create a "wine-extension-acsm.desktop" which looks like this:
Code:
[Desktop Entry]
Type=Application
Name=Adobe Digital Editions
MimeType=application/vnd.adobe.adept+xml;
Exec=env WINEPREFIX="/home/eschwartz/.wine" wine start /ProgIDOpen Adobe.ACSMessage %f
NoDisplay=true
StartupNotify=true
Icon=3455_digitaleditions.0
So xdg-open
should open *.acsm files correctly. (Without that ProgIDOpen route, well, digitaleditions.exe itself apparently does not know how to act as a file handler for ACSM.

)
Drag-and-drop: not strictly necessary.