ADE should have grabbed the file association for .acsm, but sometimes it doesn't.
Right click an example .acsm file, choose 'Open With'.
Select 'Choose defaut program'.
Select ADE. You may have to use 'More Options' and navigate to 'C:\Program Files\Adobe\Adobe Digital Editions 2.0\DigitalEditions.exe'
(or wherever your ADE is).
After that, it should work properly for all .acsm files.
Alas, there are bugs in Windows file associations that often means it wont' accept ADE as the default program.
In that case you can open any .acsm file with ADE by finding the file in File Explorer and drag-dropping it onto ADE.
Thank you, I will give this a try.
Finally--a successfuly download!!! Thanks so much--I can stop tearing my my hair out now!
For once a rare case where it isn't ADE that is to blame.