A help topic can be displayed using the topic number (HH_display_topic), but the topic must be present in the specified help file (no master is used).
Example
CmdNum = 7 /* HH_HELP_CONTEXT
FileName = 'file.chm'
EntireParam = <Topic_num>
OnDesktop = *TRUE
CALL_DLL 'VaToolBx.dll' 'VaToolBxHtmlHelp' ID_WIN0 FileName CmdNum EntireParam OnDesktop ReturnCode