Windows Help requires an application to explicitly cancel Help so that Windows Help can free any resources it used to keep track of the application and its help files. The application can do this at any time.
An application cancels Windows Help by calling the WinHelp function and specifying the HELP_QUIT value, as shown in the following example:
WinHelp(hwnd, "myhelp.hlp", HELP_QUIT, NULL);
If the application has made any calls to the WinHelp function, it must cancel Help before it closes its main window (for example, in response to the WM_DESTROY message in the main window procedure). An application needs to call WinHelp only once to cancel Help, no matter how many help files it has opened. Windows Help remains running until all applications or dynamic-link libraries that have called the WinHelp function have canceled Help.