The usual fixes
Most door problems are small: a hinge screw that pulled loose, a door that swelled in winter, a strike plate that doesn't line up. The pro tightens, shims, planes and adjusts until the door closes smoothly.
New locks
Buy a knob or lever and deadbolt that fit the holes already in your door. Most standard sets do. The pro installs them and checks they lock smoothly.
Drafts under the door
Light or cold air under an exterior door means the sweep or weatherstrip is worn. Fresh weatherstripping stops drafts and noise. If the door itself sags, the hinges need adjusting first.
Want a smart lock instead? See smart home device install.