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. 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). 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. 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.