Normally you could solder on a male pipe thread adapter and then use a female plastic adapter. If it is CPVC plastic, a compression fitting can be used if the pressure does not exceed 60 lbs. There are some special unions at Lowe's that adapt CPVC to copper.
Copper and Pvc plumbing are not interconnectable. If you live in an area where temperature changes fluctuate this connection is likely to crack and leak. It can be done but it is not adviseable
Go to a plumbing supply warehouse, and pickup an adaptor. They are usually brass to CPVC. You can sweat the brass to the copper and run PVC from the CPVC.