I have driven many times around Paris following different routes and times and think this are the options you have for driving from CDG to Vimoutiers. There is a lot of slow moving traffic getting worse during rush hour, best to avoid that.
For going to the N12 freeway south of Versailles you have to or can follow the A86 for driving around Paris. You can do that counterclockwise along the westside or clockwise along the eastside. With the first you have to go trough the Duplex toll tunnel part of the A86 east of Versailles, with the latter you can avoid that (follow A3 Nantes-Bordeaux to A86 from CDG). For the CCW option follow A1 St. Denis to A86 from CDG. Both routes have almost the same length, it depends more how lucky you will be not getting stuck in one of the Friday afternoon traffic jams.
Know that between Verneuil sur Avre (Verneuil d’Avre et d’Iton) and Vimoutiers you have to follow local roads and can easily take more time as the routeplanners tell you. That’s the downside taking the N12.
You can also take from Paris the tollroads A13 (direction Rouen) and A28 (direction Le Mans) to Vimoutiers. Follow the A86 clockwise and turn off to A14 near Nanterre (btw not to confuse with Nantes) for driving to the A13.