How can I get from CDG 7.30am to Calais ferry at 3pm on 14 april 2016?
You can take the RER B train from CDG to Gare du Nord, then take a TGV from Paris to Calais. CDG to Paris tickets are bought at the ticket window or ticket vending machines at the airport train stations. Find TGV tickets on Voyages-SNCF for the Gare du Nord - Calais TGV.
See this thread for details on getting from Calais Frethun TGV station to Calais ferry terminal.