A default file transfer application should always be available to send and receive an arbitrary file. The default application should make the received files easy to access so that the user can open, delete, or save each file. Microsoft provides a default file transfer application along with the Microsoft File Transfer API. It can be replaced with one from an alternative source or one that has been specially created
Such an application that transfers the files of all specific applications must identify itself by using the xfRegister function call to register itself as the default application.