| .K25 | Kodak K25 Image | 208 |
| .K25 | Kurzweil K2500 File | 260 |
| .K26 | Kurzweil K2600 File | 300 |
| .K2S | Kaiser 2 Saved Game | 300 |
| .K3B | K3b Disk Burning Project File | 400 |
| .K3G | 3GP Mobile Phone Video File | 270 |
| .KAG | King Arthur's Gold Map File | 450 |
| .KAL | Kratos Vision Data File | 333 |
| .KAP | BSB Chart Image File | 311 |
| .KAR | Karel Function Dictionary | 229 |
| .KAR | Karaoke MIDI File | 287 |
| .KB | C++ Keyboard Script | 318 |
| .KB2 | Kleo Backup File | 300 |
| .KBD | 3ds Max Keyboard Shortcuts File | 245 |
| .KBD | Keyboard Layout Script | 325 |
| .KBITS | Bits'N'Picas Bitmap Font File | 250 |
| .KBS | Keyboard Script File | 350 |
| .KC | KeyKit Collection | 400 |
| .KC2 | Kodak DCS200 Camera Raw Image | 300 |
| .KCB | Kindle Create Book File | 300 |
| .KCL | NIntendo Collision File | 286 |
| .KCT | Keyman Developer Customization Source File | 425 |
| .KDB | Keypass Database File | 265 |
| .KDBX | KeePass Password Database | 245 |
| .KDC | Kaspersky Virus Database File | 200 |
| .KDC | Kodak Photo-Enhancer File | 267 |
| .KDE | KryptoStorage Container File | 167 |
| .KDENLIVE | Kdenlive Project File | 200 |
| .KDEVDLG | KDevelop Dialog Box File | 300 |
| .KDEVELOP | KDevelop Project Data File | 300 |
| .KDEVPRJ | KDevelop Project File | 240 |
| .KDI | KD Player Skin Image File | 267 |
| .KDK | Kodak Proprietary Decimated TIFF File | 225 |
| .KDMP | Windows Crash Dump File | 300 |
| .KDS | KD Player Skin File | 333 |
| .KDZ | Kaspersky Virus Bases File | 156 |
| .KDZ | LG Mobile Device Firmware | 300 |
| .KEB | Kaspersky Virus Bases File | 400 |
| .KELGFILE | Best Free Keylogger Log File | 150 |
| .KES | Kurzweil 3000 Document | 243 |
| .KEXI | Kexi Database | 300 |
| .KEXIC | Kexi Database Connection File | 400 |
| .KEXIS | Kexi Database Shortcut File | 450 |
| .KEXT | Mac OS X Kernel Extension | 287 |
| .KEY | Software License Key File | 232 |
| .KEY | Security Key | 240 |
| .KEY | LightWave License File | 249 |
| .KEY | Keynote Presentation | 249 |
| .KEY | Keyboard Definition File | 276 |
| .KEY-TEF | Keynote iCloud Presentation | 275 |
| .KEYCHAIN | Mac OS X Keychain File | 230 |
| .KEYSTORE | Java Keystore File | 285 |
| .KEYTAB | Kerberos Keytab File | 333 |
| .KF2 | Max Payne Resource File | 250 |
| .KFL | Outlook Known Feed List | 450 |
| .KFM | Gamebryo 3D Model File | 250 |
| .KFN | KaraFun Karaoke File | 360 |
| .KFS | Max Payne Model File | 250 |
| .KFX | Amazon KF10 eBook File | 237 |
| .KFX | Kofax Image File | 300 |
| .KGB | KGB Archive File | 214 |
| .KGTEMP | KuGou Temporary Cache File | 450 |
| .KHD | Dynamics AX Kernel Help Data File | 233 |
| .KHI | Dynamics AX Kernel Help Index File | 300 |
| .KIC | Kodak Compressed Image File | 300 |
| .KID | Kidspiration Document | 362 |
| .KIN | Kinetic Music Project | 260 |
| .KISMAC | KisMAC Webservice File | 333 |
| .KIT | Battery Drum Kit File | 333 |
| .KIT | CodeKit File | 209 |
| .KIT | 2020 Design Live File | 314 |
| .KIX | KiXtart Script File | 271 |
| .KKK | KKK Ransomware Encrypted File | 400 |
| .KLC | Keyboard Layout Creator Source File | 467 |
| .KLG | Log File | 280 |
| .KLG | KOFIA Log | 250 |
| .KLQ | Kaspersky Quarantine File | 325 |
| .KMA | Correlate Archive File | 283 |
| .KMC | Kinemac Animation File | 267 |
| .KMCOBJ | Kinemac Sprite Object | 267 |
| .KMF | Everyone Piano Keyboard Map File | 500 |
| .KML | Keyhole Markup Language File | 223 |
| .KMM | K-Meleon Macro Module | 282 |
| .KMP | Korg Trinity/Triton Keymap File | 223 |
| .KMP | Mario Kart Wii Course Description File | 211 |
| .KMR | KnowledgeMill Link File | 400 |
| .KMS | Correlate Solutions File | 183 |
| .KMV | Mobile DJ Video File | 257 |
| .KMY | KMyMoney Data File | 200 |
| .KMZ | Google Earth Placemark File | 213 |
| .KNO | DigIN Serialized Break Model | 200 |
| .KNT | KeyNote Note File | 271 |
| .KO | Linux Kernel Module File | 267 |
| .KODAK | Kodak Photo CD File | 287 |
| .KODE | KodeFile Encrypted File | 275 |
| .KODU | Kodu Game File | 146 |
| .KON | Yahoo! Widget XML File | 285 |
| .KOOB | Koob E-Book File | 367 |
| .KOR | Windows Korean Noise-Words List File | 400 |
| .KOZ | Audiokoz Music File | 300 |
| .KOZ | Bell Music File | 300 |
| .KPF | Kindle Create Publishable File | 250 |
| .KPF | Komodo Project File | 180 |
| .KPG | Kai's Power Goo Graphic | 450 |
| .KPL | Kids Programming Language File | 286 |
| .KPL | Krita Color Palette | 200 |
| .KPL | Kazaa Playlist File | 350 |
| .KPP | Kid Pix Presentation | 400 |
| .KPR | KPresenter Presentation | 167 |
| .KPS | Keyman Developer Package Source File | 450 |
| .KPX | Kid Pix Picture | 362 |
| .KPZ | Komodo Template File | 280 |
| .KRA | Krita Image Document | 225 |
| .KRAB | GandCrab V4 Ransomware Encrypted File | 190 |
| .KRC | Mouse and Key Recorder Macro File | 333 |
| .KRZ | Kurzweil K2000 File | 280 |
| .KS | Kickstart File | 280 |
| .KS | Keystore File | 425 |
| .KSC | Korg Trinity/Triton Script File | 300 |
| .KSD | KeepSafe File | 314 |
| .KSD | Native Instruments Massive Sound File | 234 |
| .KSF | KMPlayer Skin File | 243 |
| .KSF | Korg Trinity/Triton Sample File | 312 |
| .KSH | Unix Korn Shell Script | 329 |
| .KSM | Ken Silverman Music File | 400 |
| .KSM | Pfaff Embroidery Design File | 325 |
| .KT | Kotlin Source Code File | 156 |
| .KT2 | Battery 2 Drum Kit File | 400 |
| .KT3 | Battery 3 Drum Kit File | 220 |
| .KTH | Keynote Theme | 300 |
| .KTN | KTooN Animation Project File | 400 |
| .KTP | Kinetic Project Template | 300 |
| .KTZ | Kahootz Project File | 250 |
| .KUIP | Kingsoft Office Personalization File | 300 |
| .KUX | Youku KUX Video | 400 |
| .KV | Kivy Language File | 175 |
| .KV6 | Ken's Voxlap 6 Model File | 225 |
| .KVK | Keyman On-Screen Keyboard File | 400 |
| .KVTML | KWordQuiz File | 300 |
| .KWD | KWord Document | 400 |
| .KWM | WebMoney Key File | 267 |
| .KWREPLAY | Command & Conquer 3 Replay File | 325 |
| .KX | KiXtart Tokenized Script File | 325 |
| .KXX | Keyman Developer Encrypted Keyboard File | 425 |
| .KYB | Keyboard Layout | 300 |
| .KYR | Lotus Domino Key Ring File | 300 |
| .KYS | Adobe Photoshop Keyboard Shortcuts File | 250 |
| .KZ | KuaiZip Compressed File | 365 |