anyone knows about patent,

copyright in U. S? So if we want to import a software from China, that software is already patented in China, but we need to do modification and translation on it? do we need to buy the copyright from China company, is it illegal to sell in U. S without buying copywrite from China company? or another scenario, if we just want to be their agent in U. S, do we need to apply patent for the software again in U. S? thanks in advance!!!