| .KMF | Open Source | Datové soubory | Kwalitan Memo File | Kwalitan | Open Source |
| .KMO | Unknown Developer | Datové soubory | Commercial Bank Czech Financial Data Exchange Format | Unknown Software | Unknown Developer |
| .KMS | Correlate | Datové soubory | Correlate Solutions File | Correlate | Correlate Client |
| .KMY | Open Source | Datové soubory | KMyMoney Data File | KMyMoney | Open Source |
| .KMZ | Google | Datové soubory | Google Earth Placemark File | ESRI ArcGIS for Desktop | ESRI (Environmental Systems Research Institute) |
| .KNB | Unknown Developer | Datové soubory | Neuro-Expert System Knowledge Base Data File | Neuro-Expert System | Unknown Developer |
| .KND | NEPLAN AG | Datové soubory | NEPLAN-DOS Import Or Export File | NEPLAN Electricity | NEPLAN AG |
| .KNF | Orchida Soft | Datové soubory | Orchida Knitting System Data | Orchida Knitting System | Orchida Soft |
| .KNO | EvREsearch LTD. | Datové soubory | DigIN Serialized Break Model | DigIN | EvREsearch LTD. |
| .KOC | Open Source | Datové soubory | Koha Offline Circulation Data | Koha | Open Source |
| .KOK | Recisio | Datové soubory | KaraFun Karaoke Data | KaraFun | Recisio |
| .KOS | South-Western Educational Publishing | Datové soubory | MicroType Pro Document File | MicroType Pro | South-Western Educational Publishing |
| .KPF | ActiveState | Datové soubory | Komodo Project File | ActiveState Komodo IDE | ActiveState |
| .KPP | Software MacKiev | Datové soubory | Kid Pix Presentation | Kid Pix | Software MacKiev |
| .KPR | Open Source | Datové soubory | KPresenter Presentation | KOffice | Open Source |
| .KPX | Software MacKiev | Datové soubory | Kid Pix Picture | Kid Pix | Software MacKiev |
| .KRB | SourceForge | Datové soubory | Pyke Knowledge Rule Base | Pyke | SourceForge |
| .KRC | Kra-Tronic Corporation | Datové soubory | Mouse And Key Recorder Macro File | Kra-Tronic Corporation Mouse and Key Recorder | Kra-Tronic Corporation |
| .KRF | SPARTA, Inc. | Datové soubory | DNSSEC-Tools Keyrec Data File | DNSSEC-Tools | SPARTA, Inc. |
| .KSA | Kubotek Corporation | Datové soubory | KeyCreator Settings Archive File | Kubotek USA KeyCreator | Kubotek Corporation |
| .KSM | Pfaff | Datové soubory | Pfaff Embroidery Design File Format | Embroidermodder 2 | Open Source |
| .KSP | Luxion | Datové soubory | Keyshot Package | Keyshot | Luxion |
| .KSW | Cosmic Patterns Software | Datové soubory | Kepler Workflow Document | Kepler | Cosmic Patterns Software |
| .KTE | Open Source | Datové soubory | Kite Design File | FoilMaker | Open Source |
| .KTH | Apple | Datové soubory | iWork Keynote Theme | Apple Keynote | Apple |
| .KTI | Kelvin TOP-SET | Datové soubory | Kelvin TOP-SET Investigator Data | Kelvin TOP-SET Investigator | Kelvin TOP-SET |
| .KTX | Open Source | Datové soubory | Kwalitan Data File | Kwalitan | Open Source |
| .KU | Open Source | Datové soubory | Knowledge Explorer Knowledge Representation Knowledge Unit | my Knowledge Explorer | Open Source |
| .KUF | K.Y.N.G | Datové soubory | K.Y.N.G Update Data | K.Y.N.G | K.Y.N.G |
| .KUU | K.Y.N.G | Datové soubory | K.Y.N.G Data File | K.Y.N.G | K.Y.N.G |
| .KVB | MSR Enterprises | Datové soubory | Klick-N-View Business Cards | Klick-N-View Business Cards | MSR Enterprises |
| .KVC | Open Source | Datové soubory | KVC | KVIrc | Open Source |
| .KW3 | Pacific Software Publishing, Inc. | Datové soubory | KanjiWORD Document File | KanjiWORD | Pacific Software Publishing, Inc. |
| .KWB | Open Source | Datové soubory | Kwalitan Work File | Kwalitan | Open Source |
| .KWL | KDE | Datové soubory | KWalletManager File | KWalletManager | KDE |
| .KWO | KeyWallet GbR | Datové soubory | KeyWallet Encrypted Password Storage | KeyWallet | KeyWallet GbR |
| .KWZ | Nintendo | Datové soubory | Flipnote Studio 3D Flipnote Data | Flipnote Studio 3D | Nintendo |
| .KXP | SoftKey | Datové soubory | KEY Home Gourmet Data | KEY Home Gourmet | SoftKey |
| .KY | Sage | Datové soubory | Peachtext List Manager File | Peachtext | Sage |
| .KYN | ESTsoft | Datové soubory | ALSee Thumbnail Cache | ALSee | ESTsoft |
| .KZB | Rightware | Datové soubory | Kanzi Studio Binary Data | Kanzi Studio | Rightware |
| .L | Johan Bontes | Datové soubory | Game Of Life File | Life32 | Johan Bontes |
| .L16 | JRiver | Datové soubory | JRiver Media Center File | JRiver Media Center | JRiver |
| .L2P | IBM | Datové soubory | IBM Voice Type Languages Addword Data | IBM Voice Type | IBM |
| .L5K | Rockwell Automation Inc. | Datové soubory | RSLogix 5000 File | Studio 5000 Logix Designer | Rockwell Automation Inc. |
| .L6T | Line 6 | Datové soubory | Line 6 Tone File | Line 6 Gearbox | Line 6 |
| .LA | Open Source | Datové soubory | Lossless Audio File | Nullsoft Winamp | Nullsoft |
| .LAB | Corel | Datové soubory | WordPerfect Label Definition File | Corel WordPerfect | Corel |
| .LABEL | DYMO | Datové soubory | DYMO Label File | DYMO Printers | DYMO |
| .LAC | IBM | Datové soubory | Cognos Local Authentication Cache | Cognos software | IBM |
| .LAO | Epson US | Datové soubory | EPSON SMART PANEL File | EPSON SMART PANEL | Epson US |
| .LAR | Liquid Audio Inc | Datové soubory | Liquid Audio Player Registration File Format | Liquid Audio Player | Liquid Audio Inc |
| .LARGE | Apple | Datové soubory | Golden Orchard Apple II CD Rom File | Apple OS X | Apple |
| .LAS | Various Developers | Datové soubory | LIDAR Data Exchange File | ESRI ArcGIS for Desktop | ESRI (Environmental Systems Research Institute) |
| .LAST | Valve | Datové soubory | Valve Steam Data | Steam | Valve |
| .LASXML | Unknown Developer | Datové soubory | Laser App Data Exchange | Unknown Software | Unknown Developer |
| .LAT | Leslie Lamport | Datové soubory | LaTeX File | LaTex | Leslie Lamport |
| .LAUNCHER | Apple | Datové soubory | Golden Orchard Apple II CD Rom File | Apple OS X | Apple |
| .LAV | PSU Miller Lab | Datové soubory | DNA Sequence Alignment File | LASTZ | PSU Miller Lab |
| .LAVS | Liquid Audio Inc | Datové soubory | Liquid Audio Secured Download File | Liquid Audio Player | Liquid Audio Inc |
| .LAW | E*Law Publishing Limited | Datové soubory | eLawForms | eLawForms | E*Law Publishing Limited |
| .LAY | Tecplot, Inc | Datové soubory | Tecplot Layout File | Tecplot 360 | Tecplot, Inc |
| .LAZ | Global Heavy Industries | Datové soubory | LiquidApps Project File | Liquid Studio | Global Heavy Industries |
| .LA_ | Texas Instruments, Inc. | Datové soubory | TI Databook File | TI Connect | Texas Instruments, Inc. |
| .LBA | ShopTalk Systems | Datové soubory | Liberty BASIC Source Code | Liberty Basic | ShopTalk Systems |
| .LBD | Llamagraphics | Datové soubory | Life Balance User Data File | Life Balance | Llamagraphics |
| .LBE | Llamagraphics | Datové soubory | Life Balance Xml-based Exchange Data | Life Balance | Llamagraphics |
| .LBL | Interscape | Datové soubory | Now Contact Label Template | Now Up-to-Date (Now Contact) | Now Software |
| .LBM | Electronic Arts | Datové soubory | Deluxe Paint Bitmap Image File | Canvas X | ACD Systems |
| .LBP | Schneider Electric | Datové soubory | ProWORX Nxt Logic Pointer Data | ProWORX | Schneider Electric |
| .LBR | Dag Agren, Circlesoft | Datové soubory | LU Library Archive | The Unarchiver | Dag Agren, Circlesoft |
| .LBX | Microsoft Corporation | Datové soubory | FoxPro Label File | Microsoft Visual FoxPro | Microsoft Corporation |
| .LBXLLS | Interscape | Datové soubory | Logos Libronix 3.0 Data | Logos Bible Software | Interscape |
| .LBXWKS | Libronix Corporation | Datové soubory | Libronix DLS Workspace | Digital Library System | Libronix Corporation |
| .LCC | IBM | Datové soubory | IBM Voice Type Languages Newuser File | IBM Voice Type | IBM |
| .LCD | ABBYY | Datové soubory | ABBYY Language File | ABBYY FineReader | ABBYY |
| .LCN | Microsoft Corporation | Datové soubory | License File | Microsoft Windows | Microsoft Corporation |
| .LCP | Mark Finney | Datové soubory | FARSITE Landscape Data | FARSITE | Mark Finney |
| .LCS | Swiftpage, Inc. | Datové soubory | ACT! History Data | Act! | Swiftpage, Inc. |
| .LCT | Oracle Corporation | Datové soubory | Oracle Database Configuration File | Oracle Database | Oracle Corporation |
| .LCX | Cray Inc. | Datové soubory | LC Model | Microsoft Notepad | Microsoft Corporation |
| .LD | deltaComm Development Inc | Datové soubory | Telix Long Distance Codes Data | Telix for Windows | deltaComm Development Inc |
| .LD2 | Kevin Yau | Datové soubory | Lingoes Dictionary File | Lingoes | Kevin Yau |
| .LDF | Microsoft Corporation | Datové soubory | SQL Server Transaction Log File | Microsoft SQL Server | Microsoft Corporation |
| .LDIF | Mozilla | Datové soubory | LDAP Data Interchange Format File | Mozilla Thunderbird | Mozilla |
| .LDL | Corel Corporation | Datové soubory | Corel Paradox Delivered Library File | Corel Paradox | Corel |
| .LDP | Kevin Yau | Datové soubory | Lingoes Dictionary File | Lingoes | Kevin Yau |
| .LDS | GNU Project | Datové soubory | Binutils LD Linker Script | Microsoft Notepad | Microsoft Corporation |
| .LDT | DIAL | Datové soubory | Eulumdat Formatted Luminaire Data File | DIAL DIALux | DIAL |
| .LDX | Global Heavy Industries | Datové soubory | Liquid Studio Compiled Executable | Liquid Studio | Global Heavy Industries |
| .LEGAL | DaveTech | Datové soubory | DaveTech Legal Document | Notepad++ | Don Ho |
| .LEP | CAM Development | Datové soubory | Label and Envelope Designer Plus 2000 Data File | Label and Envelope Designer Plus 2000 | CAM Development |
| .LES | David A. Wheeler | Datové soubory | Lesson File | Mklesson | David A. Wheeler |
| .LET | Genesis 2000, Inc | Datové soubory | Genesis 2000 Data | Genesis 2000 | Genesis 2000, Inc |
| .LETTER | Proofpoint, Inc. | Datové soubory | Undeliverable Mail File | Sendmail | Proofpoint, Inc. |
| .LEV | Interscape | Datové soubory | NetHack Level File | NetHack | Interscape |
| .LEX | Adobe Systems Incorporated | Datové soubory | Adobe Linguistic Library Data File | Adobe Illustrator CC | Adobe Systems Incorporated |
| .LEXT | Olympus Corporation | Datové soubory | Olympus Lext Measurement Export | Unknown Software | Unknown Developer |
| .LF | Concept Software | Datové soubory | SoftwareKey License | Protection PLUS | Concept Software |
| .LFB | Laserfiche | Datové soubory | Laserfiche Briefcase | Laserfiche Client and Server | Laserfiche |
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