| jwc | Jw_cad for DOS Document |
| jwl | Roxio Jewel Case Creator Document |
| jwrp | JoliWrite Document |
| jwrt | JoliWrite Document |
| jww | Jw_cad for Windows Document |
| jzz | Lotus Jazz Spreadsheet Document |
| k3d | K-3D Document |
| karbon | KDE Karbon Document |
| kcf | KeyCAD Drawing Document |
| kdc | Kwalitan Document |
| kdf | Kinko's Document Format File |
| kes | Kurzweil 3000 Document |
| key | iWork Keynote Presentation |
| key-tef | iWork Keynote iCloud Presentation |
| keynote | iWork Keynote Presentation |
| kfa | Serif DrawPlus Key-frame Animation |
| kfi | 3D Forgastest Editor Data |
| kfl | Microsoft Outlook Known Feed List |
| kht | Nonosoft KHOT Document |
| kia | Kidspiration Document |
| kicad_pcb | KiCad PCB Design Document |
| kid | Kidspiration Document |
| kil | Kontour Drawing Document |
| kit | 20-20 Design File |
| kmc | Kinemac Animation |
| kml | Keyhole Markup Language File |
| kmt | Kermeta Document |
| kmz | Compressed KML File |
| knk | KNK Studio Cutting Docment |
| knt | iWork Keynote Note Document |
| kpp | Kid Pix Presentation |
| kpr | KPresenter Presentation |
| kpx | Kid Pix Picture |
| krs | GEUS Document |
| ks3 | 3D Forgastest Editor Object |