I totally feel your pain. They are extremely persistent and will NEVER go away.
The only way that I've found to suppress them from populating your menus automatically is to uninstall Adobe, then reinstall it, but when it prompts you to select the programs from which PDF's can be created within, do NOT select AutoCAD.
You'll still be able to create PDFs from AutoCAD drawings, but just not from within the AutoCAD editor.