FileInfo.com - The File Extensions Resource

.ADM File Extension

File Type 1	Administrative Template File (Most common)
File Format	File
Common?	No
File Description	Template used by Microsoft Group Policies that describes where registry-based policy settings are stored in the registry; also defines the user interface that administrators see in the Group Policy Object Editor when creating or modifying Group Policy objects (GPOs)
Program(s) that open adm files	Windows: Microsoft Group Policy Object Editor

File Type 2	Portfolio Admin-Level Access Flag
File Format	File
Common?	No
File Description	File created when an Extensis Portfolio Catalog (.FDB file) is open in admin mode; should be automatically deleted when the Catalog is closed, but may be deleted manually if the file is not removed after closing the Catalog.
Program(s) that open adm files	Mac / Windows: Extensis Portfolio (created and deleted automatically - should not be opened manually)

Information from FileInfo.com - The File Extensions Resource.
http://www.fileinfo.com/extension/adm