How to create a Custom Group Policy Administrative Template to change Hide File Extensions for Known File Types

I was asked by a customer, or rather a colleague of mine took the query who passed it on to me, how you could use group policy to affect the Windows Explorer setting to hide file extensions for known file types. This isn't a setting which is directly exposed by group policy through one of the standard administrative templates.

Hence, what better way to show the example than through a blogcast. The blogcast demonstrates some important concepts.

  • If there is a registry setting being changed through Windows Explorer, you need to locate it. Yes, you can use many Internet sites, but why not find it out yourself - I show you how.
  • You need to craft a custom administrative template - I show an example.
  • You need to scratch your head for a while when you find that a setting which isn't "True Policy" isn't displayed by default in the Group Policy Object Editor.

The link to the blogcast is here  - it's just under 8 minutes and just under 3MB in size. Happy viewing.

By the way, here's the custom ADM file I used to save you re-typing it.

CATEGORY "Hide File Extensions"
 POLICY "Hide file extensions"
  KEYNAME "SoftwareMicrosoftWindowsCurrentVersionExplorerAdvanced"
   VALUENAME "HideFileExt"

Comments (3)

  1. Toby Brown says:

    Great Blogcast John!

    I have one slightly OT question though. Do you use separate software to bring up the client details e.g. hostname, IP address, OS level etc as the background on your client?

    Or do you merely design a background with all the info, and set its as your background?

  2. Thanks Toby. I use the Background Info tool from sysinternals and have the background generated dynamically – take a look here



  3. Olivier Gagnon says:


    To check witch registry setting is changed/created/deleted

    when you do something (as hiding file extension, for exemple), you can

    use a tool like regmon from This tool monitor the

    registry and show you the change. It’s even live.

    Hope you find this useful.

    Best regards,


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