Though divorced in a civilian court, one is still married in the Church. If one remarries in a civilian ceremony, one is committing adultery in the eyes of the Church. One may live that way, but not take Communion as one would be living in a state of sin. But one would not automatically be excommunicated.
Zetman:
Excellence is correct in his/her post. The relevant official statement in support of what Excellence stated can be found in the Catechism of the Catholic Church, paragraph 1665, which reads
“The remarriage of persons divorced from a living, lawful spouse contravenes the plan and law of God as taught by Christ. They are not separated from the Church, but they cannot receive Eucharistic communion. They will lead Christian lives especially by educating their children in the faith.”
So one is not “excommunicated” but must refrain from taking Holy Communion.
With that said, I think what we all should say is “welcome Home Newt”
Pax et bonum