Create a custom file extension in VB 2008

I have been doing a lot of searching on the web and cant seem to find a clear way of creating a custom file extension. I know to associate the file extension to a certain program, but how d开发者_运维百科o create a format for the custom file extension?

You can do that as well through setup application as described in Walkthrough: Deploying a Windows-based Application, and you can pick any extension you like. I prefer to use abbreviation created from application name, and try to find if this extension is not in use. If extension was in use, then old reference (link between file type and application) will be broken. Use of 4 characters extensions will help with better chance of extension to be unique.