Connecting from UA to AF at CDG
As soon as you exit your UA flight, look for ANY agent around (they're scarce!) and ask to be directed to the nearest connector bus to Air France terminal. These buses pick you up at the gate, within the secured area, and bus to the secured area of terminal 2.
This is not to be confused, though, with the public shuttles going outside of the secured area. They also go between terminals, but here you'd have to go through Customs & Immigration first, and then again through Security and Passport Control. Save yourself precious time, and take the shuttle from the arrivals gate.
Good luck!