§1. In a matter which concerns private persons alone, a judge can proceed only at the request of a party. Once a case has been legitimately introduced, however, the judge can and must proceed even ex officio in penal cases and other cases which regard the public good of the Church or the salvation of souls.
§2. Furthermore, the judge can supply for the negligence of the parties in furnishing proofs or in lodging exceptions whenever the judge considers it necessary in order to avoid a gravely unjust judgment, without prejudice to the prescripts of can. 1600.
Source: Code of Canon Law (Vatican.va)