| K25 | Sample file (Kurzweil 2500) |
| KAR | MIDI file (text+MIDI) (Karaoke) |
| KB | Program source code (Knowledge Pro) |
| KBD | Keyboard mapping script (Procomm Plus, LocoScript, Signature) |
| KBM | Keyboard mapping script (Reflection 4.0) |
| KCL | Lisp source code (Kyoto Common Lisp) |
| KDB | KeePass password management database file |
| KDC | Image (Kodak Photo-Enhancer) |
| KEX | Macro (KEDIT) |
| KEY | Datafile (Forecast Pro) |
| KFX | Image (KoFax Group 4) |
| KIZ | Digital postcard (Kodak) |
| KKW | Contains all K-keywords in the RoboHELP Help project Index Designer not associated with topics |
| KMD | Knowledge model, data |
| KML | Google Earth Placemark file |
| KMP | KeyMaP (Korg Trinity) |
| KMS | Knowledge model, shortcut |
| KMV | Knowledge model, visual |
| KOS | MicroType Pro document |
| KPL | Kids Programming Language |
| KPP | Toolpad (SmartPad) |
| KPS | Bitmap graphic (IBM KIPS) |
| KQP | Native Camera file (Konica) |
| KR1 | Sample (multi-floppy) file (Kurzweil 2000) |
| KRZ | Sample file (Kurzweil 2000) |
| KSF | Stepfile format of several Pump It Up simulators |
| KYB | Keyboard mapping (FTP) |
| KYE | Game data (Kye) |
