.ascm is Adobe Content Server message file
Key Features: .ASCM File Extension
What is an .ASCM file?
File extension ascm is probably mistyped. The right suffix name is acsm and is associated with the Adobe Content Server a server software that is used to digitally protect PDF documents and e-books.
An .acsm file stores message data used for Adobe Content Server. Adobe Digital Editions (ADE) uses acsm files to download eBooks. If you can't open eBooks in ADE, you probably need to fix acsm file associations in Windows and change it to open with Adobe Digital Editions.