THE IFR FLIGHT DEPARTED INTO OVERCAST CONDITIONS AND CLIMBED TO 4000 FEET MSL. THE FLIGHT ENCOUNTERED SEVERE TURBULENCE AND THE PLANE ENTERED A 3000 FOOT PER MINUTE RATE OF DESCENT. THE RIGHT PASSENGER DOOR AND THE LEFT EMERGENCY EXIT SEPARATED FROM THE PLANE, CAUSING DAMAGE TO THE RIGHT ENGINE NACELLE AND WING SURFACE. THE PILOT PULLED UP ABRUPTLY AND LEVELED THE WINGS. THE PLANE 'BROKE OUT' AT 2,500 MSL FEET, WITH WINGS LEVEL AND 'UNDER CONTROL.' ELECTRIC POWER WAS OFF AND THE PILOT FLEW BACK TO THE AIRPORT, LANDED, AND TAXIED TO PARKING WITHOUT FURTHER INCIDENT. THE RIGHT WING WAS CRUSHED AT THE ENGINE NACELLE, THE NACELLE WAS DENTED, BOTH WINGS WERE DISTORTED AND WRINKLED ON UPPER AND LOWER SURFACES. THE PILOT THOUGHT THE DOOR PROBABLY WAS NOT FULLY LATCHED DURING THE FLIGHT AND THE TURBULENCE MADE HIS LEG HIT THE MASTER SWITCH, TURNING OFF THE POWER. THE AREA FORECAST WARNED OF MODERATE TURBULENCE BELOW 10,000 FEET.