How the OS behaves in response to a file or protocol launch request is affected by whether a registered app exists for the request. If an installed app has a corresponding file or protocol registration, the OS immediately launches the app. If multiple installed apps are registered for the file or protocol, the user is given the choice on which app to launch.
If no installed app is registered for the file type or protocol, the user is offered the option of downloading one.
Do not register for a file or protocol association unless your app can perform a useful action with it. If your app causes the app menu to be shown too frequently, the user may choose to uninstall your app ...