In the U.S. a civil marriage is not necessary, so the Church officials do not recommend it. For baptized Catholics all civil marriages are invalid anyways. In Brazil, it is a law that one must be married civilly before any other religious authority can perform your marriage. For that reason I was married civilly here in Brazil where my Catholic marriage took place, however, we continued to live in seperate houses until the Catholic marriage took place. Whereas in the U.S., because of the difference in laws, a Catholic priest will prohibit you from a civil marriage, here in Barzil, in contrast based on the laws, a Catholic priest must see proof of your civil marriage before performing your marriage.
If I would've married in the U.S. a civil marriage is not necessary. Instead, in the U.S. you pay for a marriage licenses, which is not what we have to do in Brazil.
Protestant marriages are valid for protestants and pagan marriages are valid for pagans, but only in the natural sense, they receive no sacramental, supernatural nature. Mixed marriages outside the Catholic Church between a believing Catholic do not take any validity even in the purely natural sense.
There is an examination of conscience that asks if you have ever performed a civil marriage in the U.S. I am pretty sure it is published by the Society or an affiliate, so they consider it sinful in the U.S. where it is not necessary. Remember that in the U.S. you must get a marriage license and register your marriage by law and marrying civilly is not required if you marry in the Church.