The office uniquely committed by the Lord to Peter, the first of the apostles, and to be transmitted to his successors, abides in the bishop of the church of Rome. He is the head of the college of bishops, the vicar of Christ, and the pastor of the universal Church here on earth. Consequently, by virtue of his office, he has supreme, full, immediate and universal ordinary power in the Church, and he can always freely exercise this power (canon 331, Code of Canon Law).
Should it happen that the Roman pontiff resigns from his office, it is required for validity that the resignation be freely made and properly manifested, but it is not necessary that it be accepted by anyone (canon 332 §2).
There is neither appeal nor recourse against a judgement or a decree of the Roman pontiff (canon 333 §3).