Paddock is a fenced area, usually near a stable, used primarily for grazing horses: “Horses were left to graze in the paddock after they had run the race.”
Padlock , on the other hand, means a detachable lock with a U-shaped bar hinged at one end, designed to be passed through the staple of a hasp or a link in a chain and then snapped shut: “The thieves entered the locked house after breaking the padlock with an iron rod.”