.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. 

How to open:

You can't open .ascm files in anything else.

How to convert:

Considering this file type is a mistype, no conversion is possible. However, it may be possible to achieve conversion or export of the original ACSM file.