Priests to whom the pastoral care of some parish or of different parishes together is entrusted in solidum according to the norm of can. 517, §1: 1/ must be endowed with the qualities mentioned in can. 521; 2/ are to be appointed or installed according to the norm of the prescripts of cann. 522 and 524; 3/ obtain pastoral care only from the moment of taking possession; their moderator is placed in possession according to the norm of the prescripts of can. 527, §2; for the other priests, however, a legitimately made profession of faith replaces taking possession.
Source: Code of Canon Law (Vatican.va)