Decapping enzyme for NAD-capped RNAs: specifically hydrolyzes the nicotinamide adenine dinucleotide (NAD) cap from a subset of RNAs by removing the entire NAD moiety from the 5'-end of an NAD-capped RNA (By similarity). The NAD-cap is present at the 5'-end of some RNAs and snoRNAs. In contrast to the canonical 5'-end N7 methylguanosine (m7G) cap, the NAD cap promotes mRNA decay (By similarity). Also acts as a non-canonical decapping enzyme that removes the entire cap structure of m7G capped or incompletely capped RNAs (PubMed:26101253). Has decapping activity toward incomplete 5'-end m7G cap mRNAs such as unmethylated 5'-end-capped RNA (cap0), while it has no activity toward 2'-O-ribose methylated m7G cap (cap1) (By similarity). a 5'-end NAD(+)-phospho-ribonucleoside in mRNA + H2O = a 5'-end phospho-ribonucleoside in mRNA + H(+) + NAD(+) a 5'-end (N(7)-methyl 5'-triphosphoguanosine)-ribonucleoside-ribonucleotide in mRNA + H2O = a (N(7)-methyl 5'-triphospho-guanosine)-nucleoside + a 5'-end phospho-ribonucleoside in mRNA + H(+) Divalent metal cation. Belongs to the DXO/Dom3Z family.