Hi,
Will depend greatly on what version the runtime is and what version of FT you are running.
If you have 5.0 or higher and the runtime was saved with the necessary option to allow conversion, then it's simply a case of using the Application manager to 'Restore from Runtime' (bottom option I think). Then when restored, you can then use the App manager again to 'Archive' the same project and you have your .apa file.
There are things you can do if you are using pre FT 5.0 but it isn't for the faint hearted!!
Regards,
Rob