As you'll soon discover, it depends on the type of door. Generally, a locksmith won't break your door or lock to access your home. One small exception is that if you've invested a lot in locks, that will slightly increase the likelihood of a “destructive entry”, but a licensed locksmith normally won't need to break the lock before entering your vehicle or house. Yes, a locksmith can open the lock without damaging it.
Most locksmiths use a non-destructive way of opening the door to enter the property, ensuring that the lock or door is not damaged.