Catalyzes the interconversion between ADP-D-glycero-beta-D-manno-heptose and ADP-L-glycero-beta-D-manno-heptose via an epimerization at carbon 6 of the heptose. ADP-D-glycero-beta-D-manno-heptose = ADP-L-glycero-beta-D-manno-heptose Binds 1 NADP(+) per subunit. Nucleotide-sugar biosynthesis; ADP-L-glycero-beta-D-manno-heptose biosynthesis; ADP-L-glycero-beta-D-manno-heptose from D-glycero-beta-D-manno-heptose 7-phosphate: step 4/4. Bacterial outer membrane biogenesis; LPS core biosynthesis. Homopentamer. Contains a large N-terminal NADP-binding domain, and a smaller C-terminal substrate-binding domain. Belongs to the NAD(P)-dependent epimerase/dehydratase family. HldD subfamily.