What is an ADMX File?

How to Open, Edit, & Convert ADMX Files

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A file with the ADMX file extension is a Windows/Office Group Policy Settings XML-based file that serves as a replacement for the older ADM file type.

Introduced in Windows Vista and Windows Server 2008, ADMX files specify what registry keys in the Windows Registry are changed when a certain Group Policy setting is changed.

How To Open an ADMX File

ADMX files are structured the same as XML files and so you can follow the same open/edit rules.

In other words, any text editor, like Notepad in Windows or the free Notepad++, will open ADMX files for viewing and editing. See this list of XML editors for even more programs that can edit ADMX files.

Microsoft's ADMX Migrator tool is a free add-on to the Microsoft Management Console (MMC) that provides a GUI to edit ADMX files instead of you having to use a text editor.

Viewing an ADMX file using a text editor is for that purpose only - to view the ADMX file. You don't need to open ADMX files manually for them to be used because the Group Policy Management Console or Group Policy Object Editor is what actually utilizes the files.

ADMX files are located in the C:\Windows\PolicyDefinitions folder in Windows. To display policy settings in a specific language, ADMX files reference language-specific resource files (ADML files) in a subfolder in the same location. For example, US English Windows installs use the "en-US" subfolder to hold ADML files.

You can read more about using ADMX files to manage group policy from MSDN here, and about the differences between ADMX files and ADML files here.

How To Convert an ADMX File

I don't know of any reason, or means for that matter, to convert an ADMX file to another file format. However, you may be interested in converting another type of file to an ADMX file.

In addition to editing ADMX files, the free ADMX Migrator tool from Microsoft can convert files from ADM to ADMX.

Since ADMX files define which registry keys should be changed in order to apply a Group Policy setting, it would follow that you could convert REG files to a format that could be used by Group Policy. That procedure, explained here, uses a script in Microsoft's Visual Studio program to convert REG to ADMX and ADML.

More Information on ADMX Files

Windows Server 2012 Administrative Templates in the ADMX file format can be downloaded from Microsoft here, while Windows 10 Templates can be found here.

Group Policy Object Editor in versions of Windows and Windows Server prior to Vista and Server 2008 are unable to display ADMX files. However, all operating systems that use Group Policy are able to work with the older ADM format.