Paulin Méry is easily reached from most train stations in Paris (and hence the airports as well).
Metro Map (opens a large map in a new window)
Take the train from Charles de Caulle to Gare du Nord train station. There, change to the Metro and take the number 5 line to Place d'Italie (it's the last stop on the line, so it will be the designation for the train destination).
Take the number 5 line to Place d'Italie (it's the last stop on the line, so it will be the designation for the train destination).