What has happened is that you have selected to install the PDF add-on which will not run alongside your version of Acrobat. Without warning, the installation just uninstalls the incompatible full version of Acrobat.
I don't think you can just uninstall the add-on so you will need to uninstall Rh, reinstall Acrobat 9 then reinstall Rh deselecting the add-on.
I am not sure that will be entirely trouble free as Word has to be compatible with Acrobat and I don't know if your two versions are.
It's not a way of forcing you to upgrade but I do agree it could be handled better.
See www.grainge.org for RoboHelp and Authoring tips