I'm trying this relatively simple task with a TRichViewEdit:
rve.ApplyStyleConversion(TEXT_BOLD);
It has no effect. Can anyone suggest why that might be? I've gone through all the options and settings I can find, but I can't see what's preventing this from working.
ApplyStyleConversion calls OnStyleConversion event for each selected text item, passing its parameter (TEXT_BOLD in your case) as one of parameters to this event.
If you do not process this event, ApplyStyleConversion will do nothing. Example can be found in Demos\Editors\Editor 2\