WinHelp cannot be produced from RoboHelp HTML, it is exclusive to RoboHelp for Word. Also WinHelp needs users to download and install a viewer so it is not user friendly and is now really a legacy product.
In any case, What's This help is rarely used by anyone now. It died a death. A search of the forums may reveal some old posts.
See www.grainge.org for RoboHelp and Authoring tips