If a Jewish couple marry without a kosher ketubah (they have a document written by a reform rabbi), are they halachically married? Would they require a get if they wanted to end the marriage?
Generally, a reform or conservative marriage is not just a problem of the ketubah, rather the entire marriage is invalid. This is due to a lack of halachically kosher witnesses, which invalidates the marriage totally. In addition, In addition, they often do not understand the mechanics of Jewish marriage. In place of the husband making a halachic acquisition of his wife, they view it merely as an agreement between two people.
Nevertheless, often we will require a get in order to have no doubts and stay on the safe side. If a get is unattainable for some reason, a Rav should be contacted with the details to determine if she may remarry without a get.
Igros Moshe E:H 1:85, 4:46.
Shu”t Minchas Asher 1:72