Using Adobe DE to download library books

When I try to download ebooks from the library to DE recently I get an error message from Acrobat DC saying " Adobe acrobat reader cannot open 123456-epub.acsm either because the file type is unsupported or because the file is damaged " . This has only just started happening and is common to all sources I use for download. We recently had a Windows update and DE 4.5. When this occurred we tried reverting to DE 3.0 but the problem is the same. Can you suggest anything please?