Q. 1. What is a "prohibitive Impediment?"
A. 1. Prohibitive (impedient) impediment, apart from the "diriment impediment" are the ones which, while they do not nullify the marriage, yet it renders it unlawful. These are:
• Certain simple vows: According to Canon law # 1058, "Marriage is rendered illicit by the simple vow not to marry, the vow of virginity and perfect chastity, the vow to receive sacred orders or to embrace the religious state. No simple vow invalidates a marriage unless the Apostolic See has made a special enactment to that effect."
• Legal adoption whenever it is a prohibitory impediment under the civil law. On this matter, Canon Law # 1059 states: "The Code twice mentions adoption as an impediment to marriage; once in this canon, and again in Canon Law # 1080, thus introducing a distinction between legal adoption simply as an impediment and as an invalidating impediment. Our Canon Law # 1059 states that in countries where relationship arising from legal adoption is a prohibitive impediment by civil law, it is so also by Canon Law. This is an instance of what is called "canonization" of a Civil Law by the Church. For further explanation we refer the reader to Canon Law # 1080, which treats legal adoption as a diriment impediment."
• Mixed marriages: The Church forbids marriage with fallen-away Catholics, public sinners, excommunicated persons, etc. According to Canon Law # 1060, "The Church most severely forbids everywhere marriages between two baptized persons, one of whom is a Catholic and the other a member of a heretical or schismatic sect; if there is danger of perversion for the Catholic party or the offspring, such a union is forbidden also by divine law."
Conversion of the Non-Catholic Party: Canon Law # 1062 states that the Catholic consort is bound prudently to procure the conversion of the non-Catholic party. This obligation is based upon charity. It should be fulfilled prudently, says the Code; and hence not by force or threats. Faith is a free gift of God.
Non-Catholic Ministers Excluded: Canon Law # 1063 states that even when a dispensation from the impediment of mixed religion has been given by the Church, the parties cannot, either before or after their marriage before the Church, go, whether in person or by proxy, to a non-Catholic minister in the exercise of his office, for purpose of giving or renewing the matrimonial consent. (In other words, you cannot marry twice, once in each Church/religion.)
If the pastor knows for certain that the parties are about to violate this law, or have violated it, he shall not assist at their marriage, except for very weighty reasons, all danger of scandal being removed and the Ordinary having been consulted.
It is not, however, forbidden for the parties to present themselves before a non-Catholic minister acting as a civil magistrate, when the civil law requires it, solely to comply with a civil formality and for the sake of civil effects.
Those Catholics in the United States who are married (or attempt marriage) before a non-Catholic minister are excommunicated "latae sententiae" (automatically). Reference: Third Plenary Council of Baltimore (1884).