Have you ever noticed that many files don’t seem to work in the Preview Pane in Windows Vista’s Explorer?  Until recently the only way to work around this was a painful registry hack… but now there’s a utility that will let you easily add file types to the preview list.

This article is divided up into two sections… if you want to understand how it all works, you can read through the description of the registry hack. If you just want to get right to the utility, skip down to the bottom.

The Painful Manual Registry Hack Method

Scenario: We want to be able to preview reg hack (.reg) files.

The first thing we’ll want to do is navigate down to HKEY_CLASSES_ROOT\.reg. Once we are there, we need to check the value of the (Default) key to figure out if there is a ProgID registered, and what the name of it is.

The ProgID is used so that multiple file extensions can have the same settings without duplicating information in the registry. This way the .reg and other keys can point to the “regfile” ProgID to get all their settings.

Next you’ll need to browse down to the ProgID key, where we’ll actually apply the hack: HKEY_CLASSES_ROOT\regfile. Once you are there, create a new key called shellex under it, and then create another key under that one with this name:


This key is the unique ID that tells Windows Explorer you want to set a preview handler. Once you’ve created that key and selected it, you’ll see a new (Default) key on the right hand side which you’ll want to modify.

Double-click on the (Default) key, and use the following text for the value:


This key is the unique ID for the Windows TXT Preview Handler, which I figured out by looking under the list of currently registered Preview Handlers in the registry:


You could substitute any one of these preview handlers… if you wanted to register a media file preview handler, you could use {031EE060-67BC-460d-8847-E4A7C5E45A27} as the value instead of using the preview handler for text files.

At this point, you should be able to select a .reg file and see its contents in the Preview pane:

This same method would work for any other file type, but that could get really tedious.

Adding Preview File Types The Easy Way

Now that we know how it all works (or not, as you probably skipped down to this part), you can use the free PreviewConfig utility for Windows Vista, which is just extremely simple to use. Just select the file type on the left, and then select the handler you want for it on the right.

You can choose either plain-text or media, which will register Windows Media Player to preview the file. This is useful for non-standard files like .mkv that might play fine in Windows Media player with the right plugins, but might not preview. Click the Apply button and you are done.

Download PreviewConfig from winhelponline.com [mirror]

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Lowell is the founder and CEO of How-To Geek. He’s been running the show since creating the site back in 2006. Over the last decade, Lowell has personally written more than 1000 articles which have been viewed by over 250 million people. Prior to starting How-To Geek, Lowell spent 15 years working in IT doing consulting, cybersecurity, database management, and programming work.
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