This is what AF's website shows when offering an itinerary involving a transfer between airports in Paris:
''Your trip involves a change of airports. At your arrival in Paris, please retrieve your baggage before starting your onward travel. Air France Coaches are available for transfer between Paris Charles de Gaulle and Paris Orly airports. The cost for the transfer is not included in the price of your flight ticket. More information on www.cars-airfrance.com.''
Couldn't be any clearer...