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. 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). Preferentially acts on NAD-capped transcripts in response to environmental stress (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. Specifically degrades pre-mRNAs with a defective 5'-end m7G cap and is part of a pre-mRNA capping quality control. 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). In contrast to canonical decapping enzymes DCP2 and NUDT16, which cleave the cap within the triphosphate linkage, the decapping activity releases the entire cap structure GpppN and a 5'-end monophosphate RNA. Also has 5'-3' exoribonuclease activities: The 5'-end monophosphate RNA is then degraded by the 5'-3' exoribonuclease activity, enabling this enzyme to decap and degrade incompletely capped mRNAs. Also possesses RNA 5'-pyrophosphohydrolase activity by hydrolyzing the 5'-end triphosphate to release pyrophosphates (By similarity). Exhibits decapping activity towards FAD-capped RNAs (By similarity). Exhibits decapping activity towards dpCoA-capped RNAs in vitro (By similarity). a 5'-end NAD(+)-phospho-ribonucleoside in mRNA + H2O = a 5'-end phospho-ribonucleoside in mRNA + H(+) + NAD(+) a 5'-end NAD(+)-phospho-ribonucleoside in snoRNA + H2O = a 5'-end phospho-ribonucleoside in snoRNA + 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(+) a 5'-end FAD-phospho-ribonucleoside in mRNA + H2O = a 5'-end phospho-ribonucleoside in mRNA + FAD + H(+) a 5'-end CoA-ribonucleoside in mRNA + H2O = 3'-dephospho-CoA + a 5'-end phospho-ribonucleoside in mRNA + H(+) Binds 2 magnesium ions. Belongs to the DXO/Dom3Z family.