I will reach Paris-Charles de Gaulle Sunday evening at 7.00 PM. Is it possible to go to Saint-Malo in the same day?
Getting there by car takes about 4 hours by car but driving that much after a long flight is going to be hard. Jetlag might help or make it even harder.
A taxi would likely not even accept to drive from Rennes to St Malo. As an alternative, there are buses leaving Paris late at night and arriving at Saint Malo right in time for the breakfast. Even if the plane land at 7PM, expect some delay to cross the border and retreive your luggage.
See for instance these buses: https://shop.flixbus.fr/search?departureCity=2015&arrivalCity=4748&route=Paris-Saint-Malo&rideDate=28.04.2019&adult=1&_locale=fr&wt_eid=2155510315279605137&wt_t=1555103199941&affiliate=%28not+set%29%2C
I would consider staying in Paris over the night and ride on a TGV changing at Rennes. The first train leaves slightly before 7am and arrives at about 9h30am. In addition, it's more confortable than the bus.
There are no trains that will get you from Charles de Gaulle to Saint Malo after 19:00.
A taxi or hire car could do it.