| 1 | K25 | Kodak | Kodak K25 Image |
| 2 | K26 | N/A | Kurzweil K2600 Format |
| 3 | KAP | Maptech | Maptech BSB Map Format |
| 4 | KAR | N/A | Karaoke MIDI Format |
| 5 | KBD | Autodesk | Keyboard Layout Script |
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| 6 | KCD | N/A | Generic |
| 7 | KCL | Nintendo | Mario Kart Collision Format |
| 8 | KD | N/A | Generic |
| 9 | KDA | NovaLogic, Inc. | Nova Logic Game |
| 10 | KDB | KeePass Password Safe | Keypass Database Format |
| 11 | KDBX | KeePass Password Safe | KeePass Password Database |
| 12 | KDC | Kodak | Kodak DC120 Digital Camera RAW Image Format |
| 13 | KDK | Kodak | Kodak Proprietary Decimated TIFF Format |
| 14 | KDMP | Microsoft | Windows Crash Dump Format |
| 15 | KDZ | Kaspersky Labs | Kaspersky Virus Bases Format |
| 16 | KEXT | N/A | Mac OS X Kernel Extension |
| 17 | KEY | N/A | Licence Or Encrypted Security Format |
| 18 | KEY-TEF | Apple | Keynote ICloud Presentation |
| 19 | KEYCHAIN | Apple | Mac OS X Keychain Format |
| 20 | KEYNOTE | Apple, Inc. | IWork Keynote 06 Presentation |
| 21 | KEYSTORE | Oracle Corporation | Java Keytool Key Database |
| 22 | KEYTAB | Apple, Inc. | Unix Kerberos Encrypted Key |
| 23 | KF | N/A | The Elder Scrolls Game |
| 24 | KF8 | N/A | Amazon Kindle Format 8 |
| 25 | KFG | Adobe Systems Incorporated | Adobe Acrobat Rule |
| 26 | KFL | Microsoft Corporation | Microsoft Outlook 2007/2010 RSS Feed List |
| 27 | KFP | N/A | Generic |
| 28 | KFX | Kofax | Kofax Image Format |
| 29 | KIX | KiXtart | KiXtart Script Format |
| 30 | KL3 | N/A | KL3 source code |
| 31 | KLG | N/A | Log Format |
| 32 | KMDI | The Eclipse Foundation | Kermeta |
| 33 | KML | Google | Keyhole Markup Language Format |
| 34 | KMP | Korg | Korg Trinity/Triton Keymap Format |
| 35 | KMT | The Eclipse Foundation | Kermeta |
| 36 | KMV | N/A | Mobile DJ Video Format |
| 37 | KMY | KMyMoney | KMyMoney Data Format |
| 38 | KMZ | Google | Google Earth Placemark Format |
| 39 | KNT | KeyNote | KeyNote Note Format |
| 40 | KO | N/A | Linux Kernel Module Format |
| 41 | KODI | N/A | Kodi update data |
| 42 | KOR | Microsoft | Windows Korean Noise-Words List Format |
| 43 | KPL | Pandora TV Co., Ltd. | KMPlayer Playlist Format |
| 44 | KQP | N/A | Konica Camera Photo |
| 45 | KRZ | N/A | Kurzweil K2000 Format |
| 46 | KSDS | Native Instruments, Inc. | Absynth Kore Patch Format |
| 47 | KSF | Korg | Korg Trinity/Triton Sample Format |
| 48 | KSH | N/A | Unix Korn Shell Script |
| 49 | KSM | Ken Silverman | Ken Silverman Music Format |
| 50 | KSML | Gearbox Software | Halo Custom Edition |
| 51 | KT | JetBrains | Kotlin Source Code File |
| 52 | KT2 | Native Instruments | Battery 2 Drum Kit Format |
| 53 | KT3 | Native Instruments | Battery 3 Drum Kit Format |
| 54 | KTS | JetBrains | Kotlin Script |
| 55 | KVK | Tavultesoft | Keyman Desktop On Screen Keyboard |
| 56 | KYS | Adobe Systems | Adobe Photoshop Keyboard Shortcuts Format |
