Maybe you're packaging up a media player that processes MP3 files, or perhaps it's photo editing software that must consume JPEG files. Many applications must interact with specialized file types, and occasionally companies develop proprietary data formats that are stored in files with custom extensions. For example, Photoshop files use the .psd file extension.

In this recipe, we'll see how to set the application that we're installing as the default program to use for a certain type of file. We'll use the extension .xyz. Our application will be opened when the end user double-clicks on a file called test.xyz that we'll create.