Responsive help can be set up with filters so that only certain topics are seen when a filter is applied. However, the user can select and deselect those filters so you cannot exclude content you don't want them to see.
If you do require that sort of limitation, then you need to generate different outputs. I believe with RoboHelp Server it is possible to set up different areas with restricted access to each but again that requires different outputs. I'm not sure quite how that works as I don't use RoboHelp Server.
See www.grainge.org for free RoboHelp and Authoring information.

@petergrainge
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