| NAN | Nanoscope files (Raw Grayscale) |
| NAP | Video file (EnerGraphics) |
| NB | Text file (Nota Bene) |
| NC | Instructions for numerical control machine (CAMS) |
| NCB | Developer Studio file (Microsoft) |
| NCC | CNC (Computer Numeric Control) file (CamView 3D) |
| NCD | Change directory (Norton) |
| NCF | Internal clipboard (Lotus Notes) |
| NCH | Outlook Express folder file |
| NCO | Nero BackItUp compressed backup file |
| NDB | NetOp database (Danware Data) |
| NDO | 3D low-polygon modeler (Nendo) |
| NDX | Database file (1ACT! for Microsoft Windows) |
| NDX | Index file (dBase II-III-IV) |
| NEO | Raster graphics (Atari Neochrome) |
| NES | Emulator ROMS for game console (Nintendo) |
| NET | Netlist output file (Orcad Schematic Capture) |
| NEW | New info |
| NEZ | Emulator file used for game consoles (NES) |
| NFF | Neutral File Format |
| NFO | Infobase file (Folio) |
| NFT | Template file (Netobject Fusion) |
| NG | Online documentation database (Norton Guide) |
| NIL | Icon Library file (EasyIcons-compatible) (Norton) |
| NIST | Audio (NIST Sphere) |
| NLB | Data (Oracle 7) |
| NLM | Loadable Module (Netware) |
| NLO | NetG Skill Builder file |
| NLS | National Language Support file used for localization (for example, by Uniscape) |
| NLU | E-Mail Trigger file (Norton LiveUpdate) |
| NLX | Form (FormWorx 3.0) |
| NMEA | GPS Log Data file |
| NOD | File (Netobject Fusion) |
| NP | Project schedule (Visual Planner 3.x) |
| NPI | Source for interpreter (dBase Application Generator) |
| NRF | Data file (NICOLET) |
| NRG | Image file (Nero) |
| NRI | Nero ISO CD compilation file |
| NRL | Template (Microsoft Outlook) |
| NS2 | Database (Lotus Notes version 2) |
| NS3 | Database (Lotus Notes version 3) |
| NS4 | Database (Lotus Notes version 4) |
| NSF | Database (Lotus Notes) |
| NSO | Document file (NetObject Fusion) |
| NST | Music module (MOD) (Noise Tracker) |
| NSV | Nullsoft streaming video file that comes with Winamp |
| NT | Startup files (Microsoft Windows NT) |
| NTF | National Imagery Transmission Format file |
| NTR | Executable ASCII text file |
| NTS | Executable ASCII text file |
| NTX | Index file (CA-Clipper) |
| NUF | Message for new users (1st call) (Procomm Plus) |
| NWC | Song file (Noteworthy Composer) |
| NWS | News message (MIME RFC822) (Microsoft Outlook Express) |
| NXT | Sound file (NeXT) |
