| .k | MacroModel Chemical Modeller Output |
| .k01 | Clarion Database Key |
| .k02 | Clarion |
| .k03 | Clarion DOS Database Key |
| .k1 | DataFlex Index |
| .k10 | DataFlex Index |
| .k11 | DataFlex Index |
| .k12 | DataFlex Index |
| .k13 | DataFlex Index |
| .k14 | DataFlex Index |
| .k15 | DataFlex Index |
| .k2 | DataFlex Index |
| .k25 | Kurzweil 2500 Sample Format |
| .k26 | Kurzweil 2600 Sample Format |
| .k2p | Kryptel Encrypted |
| .k2s | Kaiser 2 Saved Game |
| .k3 | DataFlex Index |
| .k3b | K3b Burning Project Format |
| .k3g | 3GP Mobile Phone Video Format |
| .k4 | DataFlex Index |
| .k48 | Apple IOS Kernel Cache |
| .k5 | DataFlex Index |
| .k6 | DataFlex Index |
| .k7 | DataFlex Index |
| .k8 | DataFlex Index |
| .k9 | DataFlex Index |
| .ka | Karma Engine (Unreal) Asset |
| .kad | Kore User |
| .kahl | Think Pascal KAHL Text |
| .kal | KManager Calibration Data |
| .kan | Kwalitan Annotation |
| .kap | Maptech BSB Map Format |
| .kar | MIDI Karaoke Format |
| .kas | Karaoke |
| .kb | Borland C++ Keyboard Script Format |
| .kb2 | Carroll-Net Kleo Backup Format |
| .kbb | BestCrypt Key Block Backup |
| .kbd | Keyboard Script File Layout |
| .kbf | MyInfo Document |
| .kbm | Scala Keyboard Mapping |
| .kbn | TeamSpeak Keybinding |
| .kbs | Keyboard Script Saved Keystrokes Format |
| .kbx | GNU Privacy Guard Keybox |
| .kc2 | Kodak RAW Image |
| .kcf | KiSS Configuration |
| .kch | KChess Notation |
| .kci | Visual Studio .NET DB Project Indexing Settings |
| .kcl | Mario Kart Wii Collision Information Format |
| .kct | Keyman Developer Customization Source |
| .kd3 | Yayoi Kaikei Accounting Data |
| .kda | Nova Logic Game |
| .kdb | Encrypted Passwords Database Format |
| .kdbx | KeePass Password Database Format |
| .kdc | Kodak DC120 Digital Camera RAW Image Format |
| .kdd | Adobe Authorware RTF Objects Editor Knowledge Display |
| .kde | Kaspersky KryptoStorage Encrypted Format |
| .kdelnk | KDE Desktop |
| .kdenlive | Kdenlive Project Format |
| .kdevdlg | KDevelop Dialogue Box Format |
| .kdevelop | KDevelop Project Data Format |
| .kdevprj | KDevelop Project Format |
| .kdf | KARMA MW/Triton Data |
| .kdh | Chinese Academic Journals Online Full-text Database |
| .kdi | KD Player Skin Image Format |
| .kdk | Kodak Proprietary Decimated TIFF Format |
| .kdl | Kill The Deadline Storage |
| .kdmp | Microsoft Windows Crash Dump Format |
| .kdr | Kinetica Installation |
| .kds | KD Player Skin Format |
| .kdt | Medbasin Evaporation Data |
| .kdx | Google Earth Import Definition |
| .kdz | Kaspersky Anti-Virus Data Format |
| .keb | Kaspersky Anti-Virus Data Format |
| .ked | KEDIT Profile And Macro Format |
| .kep | Turbo Pascal DOS Tp19 Compressed Kepler |
| .ker | ENVI Filter Kernels |
| .kes | Kurzweil 3000 Document Format |
| .kev | JAWS Preload |
| .kex | KEDIT Profile Macro |
| .kexi | Kexi Database Format |
| .kexic | Kexi Database Connection Settings Format |
| .kexis | Kexi Database Connection Format |
| .kext | Apple Mac OS X Kernel Extension Format |
| .key | Licence Or Encrypted Security Format |
| .key-tef | Apple Keynote ICloud Presentation Format |
| .keyboard | Amaya Configuration |
| .keychain | Apple Keychain Password Format |
| .keynote | IWork Keynote 06 Presentation |
| .keystore | Java Keytool Key Database |
| .keytab | Unix Kerberos Encrypted Key |
| .kf | The Elder Scrolls Game |
| .kf8 | Amazon Kindle Format 8 |
| .kfg | Adobe Acrobat Rule |
| .kfi | 3D Forgastest Editor |
| .kfl | Microsoft Outlook 2007/2010 RSS Feed List |
| .kfm | GameBryo KFM Format |
| .kfn | KaraFun Karaoke Song Format |
| .kfs | Max Payne Model |
| .kft | Korg T-series Wave |
| .kfx | Kofax Group 4 Bitmap Graphics Format |
| .kgb | KGB Archiver Compressed Archive Format |
| .kge | KGB Archiver Encrypted Compressed Archive |
| .kgm | KeyTERRA-FIRMA Ground Model |
| .kgs | Kogeo Toolbar |
| .khd | Microsoft Dynamics AX Kernel Help Data Format |
| .khi | Microsoft Dynamics AX Kernel Help Index Format |
| .kic | Kodak Compressed Image Format |
| .kid | Kidspiration Document Format |
| .kid2 | Kid Pix |
| .kids | Kid Pix |
| .kif | AutoCAD Key Index |
| .kin | Cakewalk Kinetic Music Project Format |
| .kismac | KisMAC Web Service Format |
| .kit | 20-20 Design Kitchen Design Format |
| .kix | KiXtart Script Format |
| .kjv | TheWord Bible Software King James Version Bible |
| .kkd | K Kitchen Burning Project |
| .kkw | Adobe RoboHelp Keyword Help Project Index |
| .klc | Microsoft Keyboard Layout Creator Keyboard |
| .kld | Dungeon Keeper 2 Playable Map |
| .klf | KaloMa |
| .klg | Log Format |
| .klk | Orgadata LogiKal |
| .klm | Keyhole Markup Language (Google Earth) |
| .klp | CLIP PROJECT Terminal-strip Project |
| .klq | Kaspersky Anti-Virus Quarantine Format |
| .km | BMC Patrol |
| .kma | Correlate Archive Knowledge Map |
| .kmc | Kinemac Animation Format |
| .kmcobj | Kinemac Sprite Object Format |
| .kmd | ABSTAT For Windows Batch |
| .kmdi | Kermeta |
| .kmdr | Kommander |
| .kmf | Kwalitan Memo |
| .kml | Google Earth Keyhole Markup Language Format |
| .kmm | K-Meleon Macro Module Format |
| .kmn | Keyman Developer Source |
| .kmp | Korg Trinity Audio Format |
| .kmr | KnowledgeMill Link Format |
| .kms | Correlate Solution Topic |
| .kmt | Kermeta |
| .kmv | Mobile DJ Video Format |
| .kmx | Keyman Desktop Compiled Keyboard |
| .kmy | KMyMoney Data Format |
| .kmz | Compressed Keyhole Markup Language (Google Earth) Format |
| .knf | Orchida Knitting System |
| .knn | Clarion Database Key |
| .knnk | OmniPage |
| .kno | DigIN Serialized Break Model |
| .knt | Tranglos KeyNote Note Format |
| .knw | Live For Speed AI Knowledge |
| .ko | Linux Kernel Module Format |
| .koa | Koala Paint C64 |
| .kob | Kasemake 3D Object |
| .kodak | Kodak Photo CD Format |
| .kodu | Kodu Game Format |
| .koe | AquesTone Vocal Synthesizer Syllable |
| .kom | Kit-O-Mat 3D Model |
| .komodo | KMD |
| .kon | Yahoo! Widget XML Format |
| .koob | Koob E-Book Format |
| .kor | Korean Localization Language Format |
| .koz | Sprint Music Store Music Format |
| .kpdx | KeePass Password Database |
| .kpe | KORE Performance |
| .kpf | Komodo Project Format |
| .kpj | Keyman Developer Project |
| .kpl | KMPlayer Playlist Format |
| .kpp | Kid Pix Presentation Format |
| .kpr | KOffice KPresenter Presentation Format |
| .kps | IBM KIPS Bitmap Image Graphics |
| .kpt | KPresenter Template |
| .kpx | Kid Pix Deluxe Data Format |
| .kpz | Komodo Template Format |
| .kqp | Konica Camera Photo |
| .kr1 | Kurzweil 2000 Sample |
| .kraw | Mac OS X Kernel-RAW Image Format |
| .krc | Mouse And Key Recorder Recorded Settings |
| .krg | Sybase Adaptive Server Information |
| .krn | NBA 99 Fonts |
| .krt | Microsoft Visual FoxPro Recreation |
| .krz | Kurzweil 2000 Sample Format |
| .ks | Microsoft Works Spreadsheet Format |
| .ks-ia1 | Infinite Algebra |
| .ks3 | 3D Forgastest Editor |
| .ksc | Korg Trinity Script Format |
| .ksd | Absynth Kore Patch Format |
| .ksds | Absynth Kore Patch Format |
| .kseqs | Kestrel Sequence Database |
| .ksf | Korg Trinity Sample Format |
| .ksh | Unix Shell Script |
| .ksi | Alloy Blending System ASCII Data |
| .ksl | Karaoke Song List Creator Song List |
| .ksm | Ken Silverman Music Format |
| .ksml | Halo Custom Edition |
| .ksp | Calligra Sheets Spreadsheet |
| .kss | FabTrol MRP Template |
| .kt2 | Battery 2 Drum Kit File Format |
| .kt3 | Battery 3 Drum Kit File Format |
| .kth | Apple IWork Keynote Theme Format |
| .ktn | KTooN Animation Format |
| .kto | NetKar Pro Mid Ohio |
| .ktp | Cakewalk Kinetic Project Template |
| .ktx | Kwaitan |
| .ktz | Kahootz Project Format |
| .kv6 | Ace Of Spades Model Format |
| .kvk | Keyman Desktop On Screen Keyboard |
| .kvt | KVIrc Theme |
| .kvtml | KWordQuiz Format |
| .kvw | Google Earth Workspace |
| .kwb | Kwalitan Work |
| .kwd | KWord Document Format |
| .kwf | Delphi Pascal Chart |
| .kwl | KWalletManager |
| .kwm | WebMoney Key Format |
| .kwp | Kamban Document |
| .kwreplay | Command & Conquer 3 Replay Format |
| .kws | KeyWallet Skin |
| .kxx | Custom Keyman Engine Product |
| .kyb | Keyboard Layout Format |
| .kyn | ALSee Thumbnail Cache |
| .kyr | Lotus Domino Key Ring Format |
| .kys | Adobe Keyboard Shortcut Format |
| .kz | KuiaiZip Archive |
| .kzm | Karizma Designer Album |
| .kzx | Kerkythea Material |
