The easiest way to figure out if it is a .kepub is to look at the file extension, which should be .kepub. Obviously, you will have to apply a fix to Windows so you can actually see what type of files you have, since Windows is by default an idiot.
http://windows.microsoft.com/en-us/w...ame-extensions
Besides, it could prove quite difficult to open a DRM'ed file with an arcive program, since the encryption kind of ... welll ... ENCRYPTS the contents!!
The DRM tool shouldn't care about what's in the .kepub and so long as it's designed to decrypt .kepub, it will do so for ALL .kepubs including these.