string fileName = ....;
string appName = ....;
FormsService formsService = ....;
 
MediaFileSource source = new MediaFileSource(fileName, 
ApplicationFeed.MEDIA_SOURCE_TYPE);
 
ApplicationQuery query = formsService.CreateApplicationQuery(null);
ApplicationFeed apps = formsService.Query(query);
ApplicationEntry app = apps.CreateEntry();
app.Title.Text = appName;
app.MediaSource = source;
app = apps.Insert(app);