It's a carpenter or joiners job!
I don't like doing them because new doors need a fair bit of time to settle in and they can warp due to the different interior/exterior temperature and humidity. Most doors should be stored on site for a while to acclimatise to the humidity and spring is a good time to fit them.
I would say fitting a lock is easy if you are only aiming to do an average job! Since most locks in London seem to have been fitted by carpenters with blunt chisels.