Mont. Code Ann. § 25-15-105

If the defendant in the answer denies the judgment or provides any defense that may have arisen subsequently, the summons, with the affidavit attached, and the answer constitute the written allegations in the case. If the defendant denies liability on the obligation upon which the judgment was recovered, a copy of the original complaint and judgment, the summons, with the affidavit attached, and the answer constitute the written allegations.