ShellExecute(hwnd, "open", "file:///...", 0, 0, 0);
return TRUE;
if((ShellExecute) return FALSE){...}

SHELLEXECUTEINFO Execute;
memset(&Execute, 0, sizeof(Execute));
Execute.cbSize = sizeof(Execute);
Execute.fMask = 0;
Execute.hwnd = 0;
Execute.lpVerb = "open";
Execute.lpFile = "file:///...";
Execute.lpParameters = NULL;
Execute.lpDirectory = 0;
Execute.nShow = SW_SHOW;
Execute.hInstApp = 0;
if(ShellExecuteEx(&Execute) == 0)
{
//erreur
}