Their website is confusing. Can I just buy a ticket? Not a pass? I need to go to and from the airport and that is all.
If you won't need any form of public transportation when in Paris, then just buy a paper ticket at the RER station.
Or you could just take a taxi. From CDG taxis are a fixed fare- €56 to Right bank locations, €65 to Left bank.
Airport tickets cost 13€ and are valid to any RER/métro station. They are available in paper format.