| .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 |
File extensions are not normally displayed to users. To change this, go to Control Panel, select Appearance and Personalization and Folder Options. Next, select the View and find the option "Hide extensions for known file types". The option should be deselected (cleared) and confirmed with OK.
