Orientalium Ecclesiarum §25

²⁵ If any separated Eastern Christian should, under the guidance of the grace of the Holy Spirit, join himself to the unity of Catholics, no more should be required of him than what a bare profession of the Catholic faith demands. Eastern clerics, seeing that a valid priesthood is preserved among them, are permitted to exercise the Orders they possess on joining the unity of the Catholic Church, in accordance with the regulations established by the competent authority.