The Catholic Church regards any vaild marriage between two baptized persons as a Sacramental Marriage. So it sounds to me like they are saying they will not marry a couple who has been living together prior to marriage.
This seems to conflict with the statements about cohabitating couples on the US Confrence of Catholic Bishops website about marriage:
"If you are a cohabiting couple who has chosen to marry, the Catholic Church welcomes your decision to marry. Because cohabitation can have an effect on the marriage, couples are encouraged to explore certain questions with the pastoral minister who is preparing them for marriage. . . .Pastoral ministers may encourage cohabiting couples without children to separate for a period before marriage as a sign of their free, loving decision to follow the Church’s vision of marriage and sexuality. Couples are also encouraged to receive the Sacrament of Reconciliation. . . .People have a right to marry; therefore, cohabiting couples cannot be denied marriage in the Catholic Church solely because they are cohabiting. However, cohabitation may raise questions, for example, about the couple’s freedom to marry, that need to be explored.
foryourmarriage.org/interior_template.asp?id=20398797