i want to start winword with a doc-file based on a dot-file

the following line works :

HINSTANCE hinst = ShellExecute (NULL,"open","C:\\xxx.dot",NULL,NULL,SW_SHOW);


but not the next two lines :

HINSTANCE hinst = ShellExecute (NULL,"open","C:\\xxx.dot","/t",NULL,SW_SHOW);

HINSTANCE hinst = ShellExecute (NULL,"open","C:\\xxx.dot /t",NULL,NULL,SW_SHOW);