An application can display a Help button in any common dialog box by specifying the appropriate flag in the Flags member of the structure for that common dialog box. When the Help button is displayed, the application must process the request for help from the user. This can be done in one of the application's window procedures or in a hook function.
To have a window procedure process the request for help, the application must register the HELPMSGSTRING message identifier by calling the RegisterWindowMessage function. (This is the same as the action that the Find common dialog box needs to take to process the FINDMSGSTRING message.) The application uses the hwndOwner member of the common dialog structure in order to specify the owner for the Help window in its call to WinHelp.