| Extension | Information |
| H | ADS Include File (Autodesk, Inc.) |
| H | Header |
| H! | Flambeaux Tutorial Database |
| H++ | C++ Header File |
| H-- | Sphinx C-- Header File |
| H0 | Magix Musstu File |
| H1 | Bruker Aspect NMR Data File |
| H1 | Magix Musstu File |
| H16 | VC98 Include 16-bit File |
| H2O | Water Web Program File (Clear Methods, Inc.) |
| H32 | BC45 32-bit Include File |
| H3M | Game Map File |
| H4C | Heroes of Might and Magic Map File |
| H4R | Possible Container for .MP3 Files |
| H5 | HDF5 File (The National Center for Supercomputing Applications) |
| H5B | SuperHeat 5 Building File (Survey Design Associates Ltd.) |
| H6C | SPP File |
| HA | Compressed Archive |
| HAD | MixlleniumEngine (Haydee) Web Server Module Style File |
| HAF | HEAT Archive File |
| HAI | NTgraph Nt09b-2b EMX Library File |
| HAK | GameHack File |
| HAK | Neverwinter Nights File |
| HAL | Hyper Access Lite OS/2 Data File |
| HAL | Mortyr Archive |
| HAM | Amiga Hold and Modify Image (Amiga, Inc.) |
| HAM | Novell NetWare Disk Drivers NPA |
| HAN | Viewpoint Headline Studio |
| HAP | Hamarsoft HAP 3.x Compressed Archive |
| HAT | Formula 1 Car Race 2001 Log Hat File |
| HAT | HAT (HOORA Analysis Tool) Model |
| HAY | MixlleniumEngine (Haydee) Web Server Module Content File |
| HAZ | Flight Simulator Texture File (Microsoft) |
| HAZ | Train Simulator Hazard File (Microsoft Corporation) |
| HBB | HAHTtalk Object File |
| HBC | Home Buyers Calculator Suite |
| HBK | Hex Workshop Hex Editor Bookmark File (BreakPoint Software, Inc.) |
| HBK | Humanic Software Accounting Data |
| HBK | MathCAD Handbook (Mathsoft Engineering & Education Inc.) |
| HBK | Auto Backup Backup Archive (Han-soft Software) |
| HBM | Hotline Book Mark (Hotsprings Inc.) |
| HBX | Starmoney Macro file |
| HBZ | Starmoney Macro file |
| HC | BI/Suite Hypercube |
| HC | Header File |
| HC | High Resolution Cantone TIFF Bitmap |
| HCC | HydroCAD Stormwater Modeling System Storage Chamber Definition (HydroCAD Software Solutions LLC) |
| HCD | C Poet Examples Advanced Inc File |
| HCE | HydroCAD Stormwater Modeling System Hydrograph File (HydroCAD Software Solutions LLC) |
| HCI | HydroCAD Stormwater Modeling System IDF File (HydroCAD Software Solutions LLC) |
| HCL | Handwritten Claims Log |
| HCM | IBM HCM Configuration |
| HCOM | Macintosh Sound |
| HCP | HydroCAD Stormwater Modeling System Project File (HydroCAD Software Solutions LLC) |
| HCR | Half-fold Card File |
| HCR | IBM HCD/HCM Production Configuration |
| HCR | HydroCAD Stormwater Modeling System Rainfall Definition (HydroCAD Software Solutions LLC) |
| HCSP | Content Server Web Page (Stellent, Inc.) |
| HCSS | Hyper Color Swatch Set (SodaBush) |
| HCT | Symantec Anti-Virus Live Update File |
| HCU | HydroCAD Stormwater Modeling System Units Definition File (HydroCAD Software Solutions LLC) |
| HCW | HTML Help Workshop Conversion Wizard Macro (Microsoft) |
| HCX | Harvard Graphics Chart XL Chart (Harvard Graphics) |
| HD2 | Curious Labs Poser Hand File |
| HDA | HotDocs Auto-Assemble File (Matthew Bender & Company, a member of the LexisNexis Group) |
| HDAT | vStaticIP Data File (Phil Doyle a.k.a. MrJolly) |
| HDAT | Objective Analysis Package Data File |
| HDB | Nero HD-Backup (Nero AG) |
| HDB | ACT! History File (Best Software CRM Division) |
| HDC | HelloDOC Medical Software File (IMAGINE ditions) |
| HDD | HelloDOC Medical Software File (IMAGINE ditions) |
| HDF | Help Development Kit Help File |
| HDF | Hierarchical Data Format File |
| HDF | Procomm Plus Alternate Download File Listing |
| HDF | Amiga Hardfile Image |
| HDI | AutoCAD Heidi Device Interface (Autodesk, Inc.) |
| HDI | HelloDOC Medical Software File (IMAGINE ditions) |
| HDI | HotDocs Auto-Install File (Matthew Bender & Company, a member of the LexisNexis Group) |
| HDK | OS/2 Saved SKF Format File (IBM) |
| HDK | MAXI Disk Disk Image (Herne Data Systems Ltd.) |
| HDL | Procomm Plus Alternate Download File Listing |
| HDL | HotDocs Library File (Matthew Bender & Company, a member of the LexisNexis Group) |
| HDM | Handheld Markup Language File |
| HDML | Handheld Markup Language File |
| HDMP | WinXP Trouble Report |
| HDO | Helpdesk-One File |
| HDP | Magix Music/Video |
| HDR | Apollo HDRU |
| HDR | ArcInfo Binary |
| HDR | ArcView Header File (ESRI) |
| HDR | Egret Data File |
| HDR | MicroSim PCBoard Hole-Drill Schedule Report |
| HDR | PC-File+ Database Header |
| HDR | Photoshop (Adobe) |
| HDR | Procomm Plus Message Header |
| HDR | InstallShield Setup Header (InstallShield Software Corporation) |
| HDRU | Apollo HDRU |
| HDS | Hierarchical Data System |
| HDS | XMap Hierarchical Dataset (Delorme) |
| HDV | Formula 1 Car Race 2001 Season01 Vehicles Arrows File |
| HDW | Harvard Graphics Draw Vector Graphics (Harvard Graphics) |
| HDX | Help Index |
| HEA | Fifa 2001 Data Feart Legal Screeen |
| HEC | Grafic Pvquan Quant File |
| HED | Hi-Eddi |
| HED | HighEdit Document |
| HED | ReliaSoft RG |
| HEH | Scarlett Expert System Compiler Facts File |
| HEL | Hellbender Saved Game (Microsoft) |
| HELI | RealFlight Radio Control Airplane Description (Knife Edge Software) |
| HEP | Novell NetWare Help Librarian Data File |
| HEP | HostExplorer Telnet Session Profile (Hummingbird Ltd.) |
| HER | Grafic GIF File |
| HESSIAN | Insight II Hessian File (Accelrys Software Inc.) |
| HESSIANX | Insight II Hessian File (Accelrys Software Inc.) |
| HEX | Hex Dump |
| HEX | HUGO Game File |
| HEX | Macintosh BinHex 2.0 File |
| HEX | SPLITGRADE Upgrade File (Heiland electronic GmbH) |
| HF | HF File |
| HFA | ERDAS IMAGINE Hierarchical File Architecture (Leica Geosystems , LLC) |
| HFB | Ralcgm File |
| HFB | Hell Fighter Battle File (David Peterson) |
| HFD | HotDocs Form Document (Matthew Bender & Company, a member of the LexisNexis Group) |
| HFI | HP Font Info |
| HFO | Hollywood FX Object File (Pinnacle Systems, Inc.) |
| HFS | Macintosh Disk Image on CD |
| HFT | HotDocs Form Template (Matthew Bender & Company, a member of the LexisNexis Group) |
| HFV | Simulated Macintosh Volumes on PC Hard Drive |
| HFX | HotFax Fax (Smith Micro Software, Inc.) |
| HFX | US Robotics Rapid Comm Voice Data File |
| HFX | Harvard Graphics F/X File (Harvard Graphics) |
| HFX | Hollywood FX Special Effects File (Pinnacle Systems, Inc.) |
| HFZ | Pinnacle Studio Video Editing File |
| HGH | Star Wars - Tie Fighter High Score |
| HGL | DN Highlight Groups Definition |
| HGL | HP Graphics Language (Plotter File) |
| HGP | HighGrow (Legal Marijuana Growing Game) Plant File (Slick Software) |
| HGS | HighGrow Virtual Seed File |
| HGT | Shuttle Radar Topography Mission Data (SRTM) |
| HH | C++ Header |
| HH | HammerHead Drumloop File |
| HH | Help Topic Map File |
| HHA | HyperHub Archive (Oracle) |
| HHC | HTML Help Table of Contents (Microsoft) |
| HHC | TurboTax Contents File (Intuit) |
| HHH | Power C Precompiled Header |
| HHK | HTML Help Index (Microsoft) |
| HHL | Visual Basic File |
| HHP | HTML Help Workshop Project (Microsoft) |
| HHS | HyperHub Subkit (Oracle) |
| HHS | HTML Help Samples (Microsoft) |
| HHTML | Realmedia Adstream HTML File |
| HI | High Scores |
| HI | Spy-CD CD Search Index File |
| HI1 | Spy-CD CD Search Database File |
| HI2 | Spy-CD CD Search Database File |
| HI4 | Spy-CD CD Search Database File |
| HIA | Spy-CD CD Search Database File |
| HIB | Spy-CD CD Search Database File |
| HIC | Spy-CD CD Search Database File |
| HIF | Quicken On-line File (Intuit) |
| HIG | High Scores |
| HIH | Spy-CD CD Search Database File |
| HIM | Spy-CD CD Search Database File |
| HIN | HyperChem Molecule File (Hypercube, Inc.) |
| HIN | Spy-CD CD Search Database File |
| HIP | Spy-CD CD Search Database File |
| HIPS | Bitmap Graphic |
| HIQ | Spy-CD CD Search Database File |
| HIR | C64 Hires Bitmap Graphic |
| HIR | Hidden Icon Resource |
| HIS | DN History of Executing/Viewing/Editing |
| HIS | Insight II Dynamics Trajectory History File (Accelrys Software Inc.) |
| HIS | Spy-CD CD Search Database File |
| HIS | SOBEK Simulation History (WL | Delft Hydraulics) |
| HIT | HitPlayer Audio File |
| HIT | Nonags Dialog Killer Data File |
| HIT | The Sims Sound File (Electronic Arts (Maxis)) |
| HIV | RegShot Registry Hive File (TiANWEi) |
| HIW | Spy-CD CD Search Database File |
| HIX | System SYSUTIL File |
| HIZ | Spy-CD CD Search Database File |
| HJT | TreePad Hypertext Database File (Freebyte) |
| HK5 | ACT! Database File (Best Software CRM Division) |
| HKC | HTML-KIT Auto Complete Short-cuts |
| HKI | WinHki Compressed Archive (Hanspeter Imp) |
| HKI1 | WinHki Compressed File |
| HKI2 | WinHki Compressed File |
| HKI3 | WinHki Compressed File |
| HKT | egseing RB HK Data |
| HL$ | Compressed DOS Help File (Microsoft) |
| HLB | VAX Help Library |
| HLD | Structural Desktop Saved Data (Hold File) (Structural Desktop, Inc.) |
| HLF | BASIC QuickBAS QuickB01 File |
| HLF | FAR Manager Help File (FAR Group) |
| HLI | MOJO 620 Logo (TDK) |
| HLL | Boulderdash Game File |
| HLM | Winhelp Vbhilfe File |
| HLN | Microstation Hidden Line File |
| HLP | HP-95LX Help File |
| HLP | Stata Statistical Software Help File (Stata Corporation) |
| HLP | Windows Help File (Microsoft) |
| HLX | ATI Radeon Video Driver Support File |
| HLX | Hyperlatex File |
| HLX | Multi-Edit Help File |
| HLX | Visual C++ Syntax Coloring Instructions (Microsoft) |
| HLX | Hollex Cartridge Atari Cartridge Image File |
| HLZ | Multi-Edit Packed Help File |
| HM | Windows Help Context IDs used by MAKEHM.EXE. |
| HM2 | Help & Manual Help File Project |
| HM3 | Help & Manual Help File Project (ver 3) |
| HMA | ATRAC3plus Encoded Audio File (Sony) |
| HMF | HOOPS Metafile (Tech Soft America) |
| HMI | Descent Human Machine Interfaces MIDI File |
| HMM | Procomm Plus Alternate Mail Read Option Menu |
| HMP | Descent Human Machine Interfaces MIDI File |
| HMP | Help Magician Pro Project (Stateline Software) |
| HMP | Technics Sx KN 6000 Keyboard Home Page File |
| HMP | 3D GameStudio Terrain Entity (Conitec Corporation) |
| HMP | Frontier: First Encounters Music File |
| HMR | GeoTIFF Bitmap File (Bentley Systems, Incorporated) |
| HMS | HMS Archiware File |
| HMS | MS SMS Inventory File |
| HMS | Stentura 8000 or Stentura 8000LX Deposition File |
| HMT | HighMAT (Microsoft) |
| HMW | Homeword for DeskMate |
| HMX | MixlleniumEngine (Haydee) Web Server Module Template File |
| HM~ | Help&Manual Backup Help File Project |
| HNC | CNC Program File Heidenhain Dialog |
| HNC | NoteCenter Note File (Domas Savickas) |
| HND | Hallo Northern Sky (HNSKY) Deep Sky Database File (Han Kleijn) |
| HNE | NoteCenter Encrypted Note File (Domas Savickas) |
| HNF | Humax Receiver Settings |
| HNS | Hallo Northern Sky (HNSKY) Settings (Han Kleijn) |
| HNV | TheWord & Bible Companion Hebrew Names Version Bible |
| HO | Knowledge Explorer Knowledge Representation Hierarchy Outline |
| HO | Magix Music/Video |
| HOB | Star Trek: Birth of the Federation Ship Graphic (Atari) |
| HOC | High Octane Race Course (Fishstick Games) |
| HOF | Hall Of Fame |
| HOG | Descent Mission File |
| HOG | Lucas Arts Dark Forces WAD File |
| HOL | Personal Paint Dutch Language User Interface File (Amiga) |
| HOR | Horoscope |
| HOT | Mosaic Internet Address |
| HOT | The Sims Sound File (Electronic Arts (Maxis)) |
| HOT | eFax Messenger Fax (j2 Global Communications, Inc.) |
| HP | HP Graphics Language (Plotter) |
| HP | Thor Database Primary Hash File |
| HP$ | NTgraph Visual C Wizzard File |
| HP- | HP Distribution Binary File |
| HP-UX | HP-UNIX File |
| HP8 | HP NewWave Write ASCII Roman8 Character Set |
| HPD | Harry Potter Related |
| HPD | HotDocs PDF Document (Matthew Bender & Company, a member of the LexisNexis Group) |
| HPD | HP Document (Hewlett-Packard Development Company, L.P.) |
| HPF | HotLine Partial Download File |
| HPF | PageMaker HP LaserJet Font (Adobe) |
| HPF | NetHelp2 Project File (Netscape) |
| HPG | HP Graphics Language (Plotter) |
| HPGL | HP Graphics Language (Plotter) |
| HPH | Designer Graphics System2 File |
| HPI | GEM Font Information |
| HPI | Hemera Photo-Object Image (Hemera Technologies Inc.) |
| HPI | Total Annihilation Saved Game |
| HPJ | Help Project File |
| HPJ | HP LaserJet Print-to-File |
| HPJ | Visual Basic Help Project |
| HPK | Compressed Archive |
| HPK | HPXUpgrade Service Pack Fileset (Haliplex Communication Systems) |
| HPL | HP Graphics File |
| HPLJ | Hewlett-Packerd LaserJet Vector Image |
| HPM | HP NewWave Emm Text |
| HPM | Procomm Plus Alternate Main Menu for Privileged Users |
| HPM | Procomm Plus Alternative Menu |
| HPM | Quaestor 1.x High Performance Map |
| HPP | C++ Builder 6 Program Header (Borland Software Corporation) |
| HPP | C++ Program Header |
| HPP | Printer Control Language Vector Image (Hewlett-Packard) |
| HPP | InfoMgr Database File |
| HPP | Zortech C++ Header |
| HPPCL | Hewlett-Packard Printer Control Language Vector Image |
| HPR | RoboHELP Configuration File |
| HPR | ATLAS.ti 4.x Project File (Scientific Software Development) |
| HPR5 | ATLAS.ti 5.0 Project File (Scientific Software Development) |
| HPRJ | Heroglyph Project File (proDAD GmbH) |
| HPT | HotDocs PDF Template (Matthew Bender & Company, a member of the LexisNexis Group) |
| HPUX | HP-UNIX File |
| HPW | CompuServe Home Page Wizard |
| HP_ | Winhelp Compressed File |
| HP~ | V-help File |
| HQP | CP/M Disc Utility Information |
| HQX | Macintosh BinHex 4 Compressed Archive |
| HR | TRS 80 Graphic |
| HR2 | Curious Labs Poser Hair File |
| HR5 | Heredis 2000 Family History File (BSD CONCEPT) |
| HRC | SoftImage Model Geometry File |
| HRF | Hitachi Raster Format Graphic |
| HRH | C++ and Resources Common Header |
| HRL | Herolab EasyWin32 |
| HRM | Netmino File |
| HRM | Procomm Plus Alternate Main Menu |
| HRP | Handy Recovery Recovered Partion Information (SoftLogica LLC.) |
| HRT | Hornet Packer Module/Song |
| HRU | HRU Bitmap |
| HRV | Personal Paint Croatian Language User Interface File (Amiga) |
| HRX | Herolab EasyWin32 |
| HRZ | Slow Scan Television (SSTV) |
| HS | Hugs Source Code |
| HS | Literate Haskell Source Code File |
| HS | HSnapshot Screen Snapshot (PCNetWork) |
| HS | RAZR Flex File (Motorola, Inc.) |
| HS2 | Postering Monochrome Image |
| HSB | HALion Sampler File (Steinberg Media Technologies GmbH.) |
| HSC | HYSYS Simulation (Aspen Technology, Inc.) |
| HSC | HelpScribble Project Source (JGsoft - Just Great Software) |
| HSC | HSC Tracker 2-op FM Music File |
| HSE | Dreamweaver Snippet |
| HSF | HOOPS Stream File (Tech Soft America) |
| HSH | IIS NNTP Hash File (Microsoft) |
| HSI | Handmade Software Graphic File |
| HSI | HSI JPEG Bitmap |
| HSK | Nimbus 7 SAMS Data File |
| HSM | Assembly Language Header University of Waterloo Engineering convention. |
| HSM | The Sims Sound File (Electronic Arts (Maxis)) |
| HSP | HomeSite WWW Page Project |
| HSP | HSC Packed |
| HSQ | CAST Application Mining Suite |
| HSQ | Data File Associated with Qaz Trojan |
| HSR | RezeptAssist Import and Export File |
| HSS | Dreamweaver Snippet |
| HSS | Photoshop Hue/Saturation Information (Adobe) |
| HST | Corel QuickCorrect and Speller History File |
| HST | WordPerfect (Corel Corporation) |
| HST | History File |
| HST | Host File |
| HST | Image Alchemy Handmade Software Graphics Histogram |
| HST | Netscape History File |
| HST | Procomm Plus History File |
| HST | Symantec Anti-Virus Live Update File |
| HST | Yahoo Messenger History |
| HSZ | Handyscript Skin (Ventris, Inc.) |
| HT | HyperTerminal Data File (Hilgraeve Inc.) |
| HT | BrailleNote Visual Display File (Pulse Data International Ltd.) |
| HT3 | HTML File |
| HTA | Hemera Thumbnail Archive (Hemera Technologies Inc.) |
| HTA | Hypertext Application |
| HTA | Tonline BSW4 File |
| HTACCESS | Apache Access Configuration |
| HTB | HttpBrowser Database File |
| HTC | HTML Component |
| HTF | HTF Sounding File |
| HTF | Virtual Hypertext Font |
| HTF | WebBase File |
| HTI | WebBase File |
| HTI | Win Help Related File |
| HTM | Hypertext Markup Language |
| HTMENX | egis Encrypted HTM File (HiTRUST Inc.) |
| HTML | Hypertext Markup Language |
| HTML | Mozilla (Netscape) Bookmark File (Mozilla.org) |
| HTMLENX | egis Encrypted HTML File (HiTRUST Inc.) |
| HTMLS | Server-side HTML File |
| HTN | Micrografx Picture Publisher 8 printstyles file |
| HTR | HTML-like script |
| HTR | Motion Analysis Software Skeletal File |
| HTT | Microsoft Hypertext Template |
| HTX | Extended Hypertext Template |
| HTX | MS FrontPage Database Results HTML-like query script. |
| HTZ | HTML Editor Archive |
| HUF | Huffman Encoded/Compressed File |
| HUH | HydroCAD Stormwater Modeling System Unit Hydrograph (HydroCAD Software Solutions LLC) |
| HULL | Halflife Map Collision Hull File |
| HUN | Dataview File |
| HUN | Personal Paint Hungarian Language User Interface File (Amiga) |
| HUS | Home Embroidery Format |
| HUS | Husqvarna Designer I Embroidery Machine Format (Husqvarna Viking) |
| HUY | Eto Dlia Vas |
| HVA | Tiberian Sun Voxel Animation Control File (TiberiumSun.com) |
| HVD | chosenOS HoverNews Skin File |
| HVD | CMT Surveyor's Assistant 1.x/2.0x Job |
| HVD | HerdView Event Data File |
| HVD | ISIS Hviews File |
| HVD | HoverDesk Theme File (Hover Inc.) |
| HVX | Lightwave 3D Hypervoxel (NewTek) |
| HW | Stanford University EPGY Homework |
| HWCFG | VersaPro Hardware Configuration File |
| HWD | Hollywood Presentation File |
| HWL | Corel Shared Writing Tools 9.0 File |
| HWL | Hangman Deluxe Word List |
| HWM | Hillwalker/MapWise/Alpiniste Own Raster Map Parameters (ISYS Computers) |
| HWP | Hangul Word Processor File (Haansoft) |
| HWPROJ | Visual Studio .NET Help Project (Microsoft) |
| HWR | Hillwalker/MapWise/Alpiniste ISYS Route Card (ISYS Computers) |
| HX | EARS Component File |
| HX | THOR Database Cross-reference Hash File |
| HXC | Help 2 Project/Collection File (Microsoft) |
| HXCONV | Huelix Audio Converter Session Information (Huelix Solutions Private Ltd) |
| HXD | Help 2 Validator File (Microsoft) |
| HXF | Help 2 Include File (Microsoft) |
| HXG | Help 2 Filter Cache (Microsoft) |
| HXH | Help 2 Merged Hierarchy (Microsoft) |
| HXI | Help 2 Compiled Help File (Microsoft) |
| HXK | Help TOC/Index File |
| HXK | Help 2 Keyword Index (Microsoft) |
| HXL | Help 2 Registered Namespaces List (Microsoft) |
| HXM | Descent2 HAM File |
| HXM | Procomm Plus Alternate Protocol Selection Menu for All Users |
| HXS | Help 2 Compiled Help File (Microsoft) |
| HXT | Help TOC/Index File |
| HXT | Help 2 Table of Contents (Microsoft) |
| HXV | Help 2 Virtual Topic Definition (Microsoft) |
| HXW | Help 2 Merged Keyword Index (Microsoft) |
| HXX | C++ Header |
| HX_ | C Poet Compressed Disk1 File |
| HY1 | Ventura Publisher Hyphenation Algorithm |
| HY2 | Ventura Publisher Hyphenation Algorithm |
| HYC | WordPerfect Hyphenation File (Corel Corporation) |
| HYD | WordPerfect for Windows Hyphenation Dictionary (Corel Corporation) |
| HYP | Acrobat Spelling File (Adobe) |
| HYP | Hyper Compressed Archive |
| HYP | Hypertext File |
| HYP | Hyphenation File |
| HZ | Chinese Text |
| H_ | Winhelp Compressed File |
| H__ | C++ Header Seldom used C++ Header (same as H++ and H) |