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 (PubMed:28283058). The NAD-cap is present at the 5'-end of some RNAs and snoRNAs (By similarity). 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 and mediates their subsequent degradation (PubMed:22961381). Has decapping and 5'-3' exonuclease activities (PubMed:22961381). Has decapping activity toward incomplete 5'-end cap mRNAs such as unmethylated 5'-end-capped RNA to release GpppN and 5'-end monophosphate RNA (PubMed:22961381). The 5'-end monophosphate RNA is then degraded by the 5'-3' exoribonuclease activity, enabling this enzyme to decap and degrade incompletely capped mRNAs (PubMed:22961381). 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.