| Extension | Information |
| K | Desktop Color Separation Specification Black Layer |
| K | NRJ Live File |
| K | IRIS Editor Format File (eurobraille) |
| K00 | Tonline DB File |
| K01 | Tonline DB File |
| K01 | Clarion DOS Database Key File (SoftVelocity) |
| K02 | Tonline DB File |
| K02 | Clarion DOS Database Key File (SoftVelocity) |
| K03 | Tonline DB File |
| K03 | Clarion DOS Database Key File (SoftVelocity) |
| K04 | Clarion DOS Database Key File (SoftVelocity) |
| K05 | Clarion DOS Database Key File (SoftVelocity) |
| K06 | Clarion DOS Database Key File (SoftVelocity) |
| K07 | Clarion DOS Database Key File (SoftVelocity) |
| K08 | Clarion DOS Database Key File (SoftVelocity) |
| K09 | Clarion DOS Database Key File (SoftVelocity) |
| K1S | Wave Glib19 File |
| K2 | Kar2ouche Storyboard File |
| K25 | Kodak DC25 Digital Camera File |
| K25 | Kurzweil 2500 Sample (Kurzweil Music Systems, Inc.) |
| K3D | 3DS Macro Language Description |
| K4E | Karaoke 4 Everyone.com Player/Editor File (Karaoke 4 Everyone.com) |
| K7 | DCMO6 Emulator Tape Image |
| KAL | Sfkal Calender Kal_40 File |
| KAN | Kwalitan Annotation (Vincent Peters, Department of Research Methodology, University of Nijmegen, The Netherlands) |
| KAP | MapInfo Sea Chart |
| KAR | FOX+ 2.0 |
| KAR | Karaoke MIDI File |
| KAR | Keep-It Archive (Remember International Associates Ltd) |
| KAT | Katorzer Music Composition |
| KAU | KeyAudit Software Audit |
| KB | C++ Keyboard Script (Borland Software Corporation) |
| KB | Knowledge Pro Source Code |
| KBD | Keyboard Script File Layout (Microsoft) |
| KBF | MyInfo Documnet/Outline (Milenix Software) |
| KBI | Keirsey-Bates Temperament Sorter Index |
| KBM | Reflection Keyboard Script File Layout |
| KBM | Scala Keyboard Mapping |
| KBN | TeamSpeak Keybinding File (TeamSpeak Systems) |
| KBP | Keirsey-Bates Temperament Sorter Profile |
| KBR | Keirsey-Bates Temperament Sorter Data |
| KBR | The Drums Pro file |
| KBS | ACE Studio Model Builder |
| KCC | KeywordConvert Keyword/Phrase Combine List (FormatBlue Software) |
| KCF | KiSS Configuration File |
| KCH | KChess Notation File (Ark Angles) |
| KCL | Kyoto Common LISP Source Code |
| KCL | KeywordConvert Keyword/Phrase List (FormatBlue Software) |
| KCO | Kwalitan Codes (Vincent Peters, Department of Research Methodology, University of Nijmegen, The Netherlands) |
| KCP | Keychamp File |
| KCT | Kwalitan Categories (Vincent Peters, Department of Research Methodology, University of Nijmegen, The Netherlands) |
| KDB | kinodb File (datb) |
| KDB | KeePass Password Database (Dominik Reichl) |
| KDB | kusziDataBase Database File (kusziNET) |
| KDB | Doobs Database (Kyuran's World) |
| KDC | Kodak Photo-Enhancer/Photogen File |
| KDC | Kwalitan Document (Vincent Peters, Department of Research Methodology, University of Nijmegen, The Netherlands) |
| KDELNK | KDE Desktop |
| KDF | Kinkos Photo (Kinko's, Inc.) |
| KDF | VisiQuest (Khoros) Standard Data Format (AccuSoft) |
| KDH | CAJViewer |
| KDK | Kodak Proprietary Decimated TIFF Format |
| KDO | Kudo Picture Browser |
| KDT | Medbasin Evaporation Data (National Technical University of Athens, Laboratory of Reclamation Works & Water Resources Management) |
| KE$ | Modem Bitware Fax Disk2 File |
| KED | KEDIT Profile and Macro File |
| KEN | Player CDcheck Compressed File |
| KEP | Turbo Pascal DOS TP19 Compressed Kepler File (Borland Software Corporation) |
| KEP | SapShow Training File (SAP) |
| KES | Kurzweil 1000 and 3000 Accessible Documents (Kurzweil Educational Systems, Inc.) |
| KEV | JAWS for Windows Preload File (Freedom Scientific) |
| KEX | KEDIT Macro File |
| KEXI | Kexi Native Database File (KDE e.V.) |
| KEXIS | Kexi Database Connection Parameter File (KDE e.V.) |
| KEXT | Mac OS X Kernel Extension (Apple) |
| KEY | OS/2 Archive .KEY-file |
| KEY | ArcView Geocoding Matching Keys (ESRI) |
| KEY | DataCAD Icon Toolbar File (DATACAD LLC) |
| KEY | Diablo II Key File (Blizzard Entertainment) |
| KEY | Forecast Pro Datafile |
| KEY | FractInt Demo Script |
| KEY | Infinity Game Engine Directory of Resources, Locations and Types (BioWare Corp.) |
| KEY | Keyboard Definition File |
| KEY | National Construction Estimator 32 Costbook Key File |
| KEY | Program Security or Registration File |
| KEY | Sentry 2020 Encryption File |
| KEY | TBAV File |
| KEY | Top Secret Crypto Gold (TAN$TAAFL Software Company) |
| KEY | Business Key Accounting File (Universal Systems) |
| KEY | Keynote Presentation Wrapper Folder (Apple Computer) |
| KEY | AntiVir PersonalEdition License Key File (AntiVir PersonalProducts GmbH) |
| KEYBOARD | Amaya Configuration |
| KE_ | Ntgraph Ze32v215 File |
| KF2 | Max Payne Model File (Rockstar Games) |
| KFA | Dark Age of Camelot Animation |
| KFA | IRIS Shortened Format (eurobraille) |
| KFI | IRIS Native Data File (eurobraille) |
| KFL | Kwalitan Filter (Vincent Peters, Department of Research Methodology, University of Nijmegen, The Netherlands) |
| KFL | KFLog Airfield File |
| KFL | IRIS Literary (eurobraille) |
| KFL | Pegasus Mail Auto-Reply Memory File (David Harris) |
| KFM | KEY Form Designer Form Design (Broderbund) |
| KFN | KaraFun Karaoke Song (RECISIO S.A.R.L.) |
| KFP | Kinkos File Prep Tool |
| KFS | Max Payne Model File (Rockstar Games) |
| KFS | Pegasus Mail Static Kill File (David Harris) |
| KFT | Matrox X Tools Keyframe (Matrox Electronic Systems Ltd.) |
| KFX | 2D Graphic |
| KFX | KoFax Group 4 Image |
| KGB | Kremlin Encrypt File |
| KGB | Z80 Spectrum Emulator Snap/File Formats |
| KGP | Image |
| KHF | Kwalitan Tree Structure (Vincent Peters, Department of Research Methodology, University of Nijmegen, The Netherlands) |
| KHS | Kwalitan History (Vincent Peters, Department of Research Methodology, University of Nijmegen, The Netherlands) |
| KIC | Kodak Image Compression File (Eastman Kodak Company) |
| KID | Tonline Bsw4 Install Mdmimp File |
| KID | Kidspiration (Inspiration Software, Inc.) |
| KIF | AutoCAD Key Index (Autodesk, Inc.) |
| KIF | Knowledge Interchange Format Draft Proposition |
| KIL | Interview File |
| KIM | Commodore KIM-1 Program Image File |
| KIN | Kinemage Chemical Test |
| KIN | Protein Structure |
| KIP | OA-KIP Client Data Transfer File (van Ovost Automatisering b.v.) |
| KIT | Power Chord Drum Kit |
| KIT | Raven Toolkit File |
| KIT | Battery Drum Kit (Native Instruments) |
| KIX | KiXtart Script |
| KIZ | Kodak Digital Postcard File |
| KIZ | UUencoded File |
| KJV | TheWord & Bible Companion King James Version Bible |
| KKT | TTSKONE |
| KKW | RoboHELP Keyword Help Project Index File |
| KLB | GraphicWorks Album |
| KLB | Klemmbretter |
| KLD | Dungeon Keeper 2 Playable Map (Electronic Arts, Inc.) |
| KLI | KalKulator Linear Algebra File |
| KLIP | KlipFolio Klip (serence inc.) |
| KLN | COLOGNE Multilingual Transliteration Scheme |
| KM | BMC Software Patrol File |
| KM2 | ActiveModeler Professional Process Map (KAISHA-Tec Co. Ltd.) |
| KMA | Kodak Memory Album |
| KMD | ABSTAT for Windows Batch File (AndersonBell Corp) |
| KMD | AIMAX Keyboard Macro (TA Engineering) |
| KMD | Clicker Module Output |
| KMD | Media Desktop File (Kaaza) |
| KMD | Model Browser File (Metis) |
| KMF | Kwalitan Memo (Vincent Peters, Department of Research Methodology, University of Nijmegen, The Netherlands) |
| KML | Emu48 Emulator Keyboard Configuration File |
| KML | HP48 Emulator Win48 Script |
| KML | Kedit Macro Library |
| KML | Keyhole Placemark (Google) |
| KML | Google Earth Placemark (Google) |
| KMN | SIL Hebrew Font System Keyboard |
| KMP | Korg Trinity KeyMaP File |
| KMP | Knowledge Manager Knowledge Base Compressed Map (Hypersoft-net) |
| KMS | Model Browser Shortcut (Metis) |
| KMV | Model Browser File (Metis) |
| KMZ | Google Earth Saved Working Session (Google) |
| KM_ | Seqmax Seqprest Compressed Audio File |
| KNF | Personal Knowbase Custom Import Filter (Bitsmith Software) |
| KNF | Universal Flat Knitting Machine Pattern Design |
| KNF | Orchida Knitting System (Orchida Soft) |
| KNN | Clarion for Windows Database Key (SoftVelocity) |
| KNO | Personal Knowbase Data (Bitsmith Software) |
| KNW | Known Problems |
| KO | IBM/Tools/Updater File |
| KOA | Koala Paint C64 Bitmap |
| KOD | Code |
| KOE | Turbo Pascal DOS File (Borland Software Corporation) |
| KOK | DEL MP3 Karaoke |
| KOM | Kit-O-Mat 3D Model File (KingMill Enterprises LLC) |
| KON | Konfabulator Widget Code (Konfabulator) |
| KOR | Korean Text File |
| KOR | Correction File |
| KOS | MicroType Pro Document |
| KOSIMA | Kosima File |
| KPD | Kapital Database File (K Software) |
| KPF | Kapere |
| KPG | Kai'S Power Goo Graphic |
| KPJ | K Database Magic Project File (Sandor Kovacs) |
| KPL | Kazaa Playlist |
| KPL | KPL Source Code |
| KPP | Kudo Place Pack, Place Module |
| KPP | SmartPad Toolpad |
| KPP | Kid Pix Deluxe Slide Show (Broderbund) |
| KPR | Fifa World Cup Game Data Comon be File |
| KPR | KPresenter Slide Show (KOffice Web Team) |
| KPR | Kwalitan Project (Vincent Peters, Department of Research Methodology, University of Nijmegen, The Netherlands) |
| KPS | IBM KIPS Bitmap |
| KPT | KPresenter Template (KOffice Web Team) |
| KPX | Kid Pix Deluxe Data File (Broderbund) |
| KQL | Kyle's Quest Level Editor Graphic (Crimson Fire Entertainment) |
| KQP | Konica Quality Picture |
| KR1 | Kurzweil 2000 Sample (Kurzweil Music Systems, Inc.) |
| KRA | Krita Image (The KDE Project) |
| KRC | Mouse and Key Recorder Recorded File (Kra-Tronic Corporation) |
| KRIS | Kris Tracker Format Song |
| KRISTAL | KRISTAL Audio Engine Project File (Kreatives.org) |
| KRN | NBA99 Ice Hockey Foreground Font |
| KRP | HiCAD 3D Part File (ISD Benelux B.V.) |
| KRX | Karaoke MIDI File |
| KRY | Herolab Krypten |
| KRZ | Kurzweil 2000 Sample (Kurzweil Music Systems, Inc.) |
| KS | Works Sheet (Microsoft) |
| KS | SOF Game File Log |
| KSC | Korg Trinity Script |
| KSE | Keepsake Studio Export File |
| KSF | Korg Trinity Sample |
| KSF | Kick it Up Stepfiles |
| KSG | Kwalitan Segment (Vincent Peters, Department of Research Methodology, University of Nijmegen, The Netherlands) |
| KSH | Prodigy Internet Registration File |
| KSH | UNIX Shell Script |
| KSH | Dazzle Dazzle Realization |
| KSHRC | UNIX Kom Shell Environment File |
| KSL | Karaoke Song List Creator Song List (Airwer) |
| KSM | Kefrens-Sound Machine Format Song |
| KSM | Embroidery File Format for Pfaff Machines |
| KSM | Ken Silverman Music Format |
| KSS | K-ForCE Scoresheet File (Stephan Rakonza) |
| KSS | KDE [UNIX/Linux Desktop] Screen Saver (KDE) |
| KSS | MSX Music File |
| KST | Olivetti Olitext Plus Script File |
| KSW | Kepler Scientific Workflows (Kepler Project) |
| KT2 | BATTERY 2 Drum Kit (Native Instruments) |
| KTI | Kelvin TOP-SET Investigator Investigation Data (The Kelvin Consultants Limited) |
| KTK | Kutoka's Mia |
| KTP | Clarion for Windows Temporary Key File (SoftVelocity) |
| KTT | KeyText Data File |
| KTX | Kwalitan Text (Vincent Peters, Department of Research Methodology, University of Nijmegen, The Netherlands) |
| KU | Knowledge Explorer Knowledge Representation Knowledge Unit |
| KUMAC | Physics Analysis Workstation Macro File |
| KUP | Karaoke Song List Creator (Airwer) |
| KVB | Klick-N-View Business Cards |
| KVQ | Sega Smash Pack PC Version File (Sega) |
| KVT | BASIC QuickBAS QuickB03 File |
| KVW | Google Earth Workspace (Google) |
| KW$ | NTgraph Visual C Wizzard File |
| KWB | KeyWord Braille File (Pulse Data International Ltd) |
| KWB | Kwalitan Workfile (Vincent Peters, Department of Research Methodology, University of Nijmegen, The Netherlands) |
| KWD | Keyword |
| KWD | KWord File |
| KWD | Dungeon Keeper 2 Playable Map (Electronic Arts, Inc.) |
| KWF | Delphi Pascal Chart |
| KWF | Kartex |
| KWF | Kwalitan Word List (Vincent Peters, Department of Research Methodology, University of Nijmegen, The Netherlands) |
| KWI | Navigation System Data File (KIWI Format) |
| KWS | Kyocera Ringtone |
| KXS | Kexis Lossless Compressed Audio |
| KY | Peachtext List Manager (Peachtree Software (Sage Software SB, Inc.)) |
| KYB | Keyboard Layout |
| KYE | Kye Game Data |
| KYF | Visual-Voice Mouth Movement File |
| KYS | SourceOffSite Server Keys |
| KYS | Photoshop CS Keyboard Shortcut (Adobe) |
| KYS | Premiere Keys File (Adobe Systems Inc.) |
| KZP | Kazoo3D or KazooStudio KazooPicture |