New doors go through a period of adjustment in a new home, reacting to changes in humidity and temperature. Over the course of the first year in a home, a new door will often change size and shape in slight ways as the forces of nature cause it to expand and contract. These changes can lead to doors sticking in their frames.
Fixing sticking doors is usually an easy job that a handyman or carpenter can undertake. Some doors need rehanging, a process in which the handyman removes the door, repositions the hinges and reinstalls the door on the same hinges. For houses that have large fluctuations in humidity or temperature during the year, adjustable hinges that you can adjust throughout the year are ideal. Likewise, you can reposition the door's lock or knob if either of these parts are causing the door to stick in the frame.
Shaving down some doors can often help make a door fit. If the new door is a little too large, or hangs at an angle with the old door frame in which it is rubbing part of the frame or the floor, a carpenter can plane the edges of the door to fit the frame. Planing the door frame so that the door swings easily is another potential solution.
New doors also get stuck on extra layers of paint in old houses. Every time a homeowner paints a door frame, it becomes a little bit thicker, making the opening is smaller. Removing layers of old paint allows for more space for a new door to fit. Installing carpet beneath a new door will also cause the door to stick. Carpet will wear down over time, or you can install a carpet transition strip in the doorways in which the door sticks.