I thought we were talking about someone who had made the decision to no longer be in full communion with the Roman Catholic Church and thus in effect had become a Protestant. Is it the case that a Protestant who had once been a Roman Catholic and a Protestant who had been baptized by a Protestant minister are regarded differently by the Canon Law of the Roman Church?
The basics, in a nutshell:
Three kinds of marriage: sacramental, natural, and invalid.
For a Catholic to marry at all requires his bishop’s permission. If he/she is marrying a catholic of the opposite gender, and the witness is a Cleric (ordained minister) of the Catholic Church, it’s presumed to be a valid sacramental marriage and the permission is also presumed by canon law. Catholics are not permitted to have non-sacramental marriages.
For Orthodox, two orthodox, one man and one woman, whose marriage was celebrated by an Orthodox Cleric is presumed sacramentally married.
For non-Catholics, a legal marriage between a man and a woman is presumed to be a valid natural marriage. If they convert, it then becomes a sacramental marriage.
Any other case is wrong - it’s not a marriage at all in the eyes of the church, but a sham.
Natural marriages can be disolved by competent authority; sacramental cannot.
Annulments are a finding that the sacramental marriage didn’t exist - not a disolution of a sacramental marriage, but a finding that the marriage was, at best, a natural marriage, if not even lacking that, and thus is not “permanent” in the eyes of the church.
A former catholic cannot be the church’s witness normally - a special delegation would be required by the individual’s bishop, who might require another Catholic witness the exchange of vows. Also, in such cases, the bishop’s permission is not automatic, and each case is reviewed at outset.
Likewise, a catholic marrying a non-catholic cannot be presumed to have the bishop’s permission - the bishop has to give explicit permission.