I'm searching for footprint of DC Jack connector.i downloaded it from a site but its drill hole is round.can I change it to rectangular using library manager ??or please help me to download a new library.
Using round holes is most likely a concession to simple layout post process and PCB manufacturing, it avoids to think about available methods for milled slots and respective negotiations with manufacturer. Unless you are targetting to high volume mass production, round holes are just O.K. and making your life easier.