VEHICLE WAS IN PARK, SHUT OFF, KEYS ON FRONT SEAT WITH PURSE. WENT TO SEAT BEHIND DRIVER TAKING ITEMS OUT AND WENT ABOUT DOOING MY ERRAND. BOTH DOORS LEFT OPEN. UPON RETURNING, NOTICEC VEHICLE ROLLING TOWARDS HIGHWAY. TRIED TO CATCH IT WHEN SECOND DOOR KNOCKED ME DOWN AND REAR DRIVERS SIDE WHEEL WENT OVER MY FOOT.