declare
AppID PLS_INTEGER;
Command_File varchar2(100) := '"C:\Program Files\Microsoft Office\office12\WinWord.exe"';
File_name varchar2(500) := '"Your_file_name.ext"';

begin

IF(GET_APPLICATION_PROPERTY(USER_INTERFACE) = 'WEB') then
 --IF YOU DON'T WANT TO SPECIFY THE APPLICATION TO LAUNCH,BUT ONLY THE FILENAME,WITH ANY EXTENSION,THEN WINDOWS FINDS THE ASSOCIATION FOR YOU
 AppID := DDE.App_Begin('rundll32.exe url.dll, FileProtocolHandler "Your_file_name.ext"',DDE.App_Mode_Normal);

 --OR, IF YOU WANT TO SPECIFY THE APPLICATION TO LAUNCH (THE PATH OF APPLICATION MIGHT VARY FROM MACHINE TO MACHINE,PAY ATTENTION)
 --AppID := DDE.App_Begin('C:\Program Files\Microsoft Office\office12\WinWord.exe "Your_file_name.doc"',DDE.APP_MODE_NORMAL);

 --you can use also the following, but in my tests not always works (the port of application server might vary,in my case is 8889)
 --WEB.SHOW_DOCUMENT('protocol://<machine-name-of-application-server>:8889/forms/java/<Your_file_name.ext>', '_blank'); --not always works,e.g. for word documents

 synchronize;

else
 --tipically this branch is in case you have an 'old' client/server app, like in forms 6i
 HOST('cmd /c rundll32.exe url.dll, FileProtocolHandler "Your_file_name.ext"');
 --OR
 --HOST('cmd /c start C:\Program Files\Microsoft Office\office12\WinWord.exe "Your_file_name.doc"');

end if;

IF Form_Success THEN 
 Message('command executed.'); 
ELSE 
 Message('there was a problem executing command.'); 
END IF; 

EXCEPTION
	WHEN DDE.DDE_APP_FAILURE THEN
		MESSAGE('WINDOWS APPLICATION CANNOT START.');
	WHEN DDE.DDE_PARAM_ERR THEN
		MESSAGE('A NULL VALUE WAS PASSED TO DDE');
	WHEN DDE.DMLERR_NO_CONV_ESTABLISHED THEN
		MESSAGE('DDE CANNOT ESTABLISH A CONVERSATION');
	WHEN DDE.DMLERR_NOTPROCESSED THEN
		MESSAGE('A TRANSACTION FAILED'); 
	when others then
		message('ERRORE: '||sqlcode||', '||sqlerrm);
		raise form_trigger_failure;		
end;