Adobe Digital Editions 4.5.11

[Selma5C3F]

I'm having trouble with Adobe Digital Editions

I bought an e-book online and was told to download Adobe Digital Editions in order to read the book, but when i download the book and open the file the book doesn't show in Adobe Digital Editions

I can't seem to open the book in the app and I don't know what to do, I even called the store where i bought the book but they say the file is not damaged, etc.

Im using Digital Edition 4.5.11 for Mac, and have macOS Big Sur. 

I tried downloading the 3.0 version but when the download was finished i was unable to open the app because the version was too old for the system

I find it pretty weird because when i click on the downloaded file (book), it sort of sends me off to the Adobe Digital Editions app as if the book will appear there but i does not I can't find the book anywhere. 

Does anybody have any ideas as to why I cannot find my book in the app?