If when you installed Rh10 you had selected the PDF Add-on, you likely would not have Acrobat 9 still installed. See Using RoboHelp 10 on my site.
The fact that you say Acrobat 9 is functioning correctly suggests that you did not select the add-on. I suspect that is why the settings option is not enabled.
That does not stop you generating a PDF. First, it may work without changing any settings. If not, generate to Word and then generate to PDF from there. That is what RoboHelp is doing behind the scenes.
Typically and document generated from any HTML program needs some cleaning up in Word first, if only to tidy up page breaks.
See www.grainge.org for RoboHelp and Authoring tips