Catalyzes the isomeration of CDP-paratose to CDP-tyvelose. CDP-alpha-D-paratose = CDP-3,6-dideoxy-alpha-D-mannose Binds 1 NAD(+) per subunit. Nucleotide-sugar biosynthesis; CDP-3,6-dideoxy-D-mannose biosynthesis; CDP-3,6-dideoxy-D-mannose from CTP and alpha-D-glucose 1-phosphate: step 5/5. Homotetramer. Belongs to the NAD(P)-dependent epimerase/dehydratase family.