This article explains what an ADMX file is and how to use it in Windows.
A file with the ADMX file extension is a Windows Group Policy Administrative Template. This XML file serves as a replacement for the older ADM file type.
ADMX files, introduced in Windows Vista and Windows Server 2008, specify which registry keys in the Windows registry are modified when a particular Group Policy setting is changed.
For example, a single ADMX file can prevent users from accessing a web browser. The information for this block is contained in the ADMX file, which in turn is reflected in the registry.