O.o You try this:
Download Digital Edition Herunterladen | Adobe Digital Editions
Save the file in your Desk.
Then douple click on the file to make the installation.
If you get a successfully installation you should found it under finder > applications.
Thanks Nanaky - I have been able to finally download ADE 4.5 but now when I try to open the books I had purchased it gives me the error message: Activation Server Error - code E_ADEPT_INTERNAL Digital Editions encounter an error on the activation server.
Has you authorize Digital Edition berfore you download the eBook?
How do you authorize it? "Authorize Computer" is greyed out and I cannot use it. When I look at "Authorization Information", it says that my computer is authorized.
And display your Adobe ID?
I had that problem and resolved it please check out my post in unable to unauthorize Adobe ID under my name. It might work for you