| Extension | Summary |
|---|
| .H | C/C++/Objective-C Header File |
| .H0 | Movie Edit Pro Waveform Information File |
| .H10 | At Home Canada 2010 Tax Return |
| .H11 | At Home Canada 2011 Tax Return |
| .H12 | At Home Canada 2012 Tax Return |
| .H13 | H&R Block Canada 2013 Tax Return |
| .H14 | H&R Block Canada 2014 Tax Return |
| .H15 | H&R Block Canada 2015 Tax Return |
| .H16 | H&R Block Canada 2016 Tax Return |
| .H17 | H&R Block Canada 2017 Tax Return |
| .H1Q | Microsoft Help Merged Query Index File |
| .H1S | Windows Assistance Platform Help File |
| .H263 | H.263 Video |
| .H264 | H.264 Encoded Video File |
| .H265 | H.265 Video |
| .H2O | Battle Realms Game Data File |
| .H2P | Zebra2 Preset |
| .H2W | H2testw File |
| .H3 | Nintendo Wii U Hash File |
| .H3B | Line 6 POD HD300 Edit Bundle |
| .H3E | Line 6 POD HD300 Edit Preset File |
| .H3M | Heroes 3 Map File |
| .H4 | Hierarchical Data Format File |
| .H4B | Line 6 POD HD400 Edit Bundle |
| .H4E | Line 6 POD HD400 Edit Preset File |
| .H4R | Heroes of Might and Magic IV Data File |
| .H5 | Hierarchical Data Format 5 File |
| .H5B | Line 6 POD HD500 Edit Bundle |
| .H5E | Line 6 POD HD500 Edit Preset File |
| .H5M | Heroes of Might and Magic V Map |
| .H5P | HTML5 Content Package |
| .H5S | Line 6 POD HD500 Edit Setlist File |
| .H5U | Heroes of Might and Magic V Mod File |
| .H6X | Soft6502 Trainer/Simulator Hex File |
| .H77T | MGD77T Header File |
| .HA | HA Compressed Archive |
| .HAAS | Everfine LED Lamp Test Results File |
| .HAL | HansaWorld Application Language File |
| .HAM | Descent 2 Resource File |
| .HAMBU | RGTW Game Map File |
| .HAML | Haml Source Code File |
| .HAN | Amazon Kindle eBook Data File |
| .HANDLEBARS | Handlebars Template |
| .HAR | HTTP Archive FIle |
| .HAS | Haskell Script |
| .HAT | A Hat in Time Save File |
| .HBB | Line 6 POD HD Edit Bundle |
| .HBC | HyperBac Compressed Archive |
| .HBC2 | HyperBac Compressed File Archive |
| .HBE | HyperBac Compressed and Encrypted Archive |
| .HBK | Mathcad Handbook File |
| .HBS | Handlebars Template |
| .HBX | BinHex Encoded File |
| .HC | Holy C Source Code File |
| .HCA | High Compression Audio File |
| .HCC | HydroCAD Prefab Chamber Data File |
| .HCD | Samsung Android Firmware File |
| .HCDT | Thinkfree Office NEO Cell Template |
| .HCE | HydroCAD Hydrograph Data File |
| .HCF | Compact Ham Library |
| .HCI | HydroCAD IDF Data File |
| .HCL | HotDocs Clause Archive |
| .HCP | HydroCAD Project File |
| .HCR | Half-Fold Card File |
| .HCU | Hydrograph Units Definitons File |
| .HCX | ChartXL Chart |
| .HCXS | Canadian Product Incident Report Form |
| .HD2 | Poser Hand Pose File |
| .HD3D | Home Design 3D Project |
| .HDA | HotDocs Auto-Assemble File |
| .HDB | HansaWorld Database File |
| .HDD | Parallels Desktop Hard Disk File |
| .HDF | Hierarchical Data Format File |
| .HDI | Hard Disk Image |
| .HDK | HotDocs Registration File |
| .HDL | HotDocs Library File |
| .HDM | HDML File |
| .HDML | Handheld Device Markup Language File |
| .HDMOV | QuickTime HD Movie File |
| .HDMP | Windows Heap Dump |
| .HDP | HD Photo File |
| .HDPMX | HotDocs Publisher Mapping XML File |
| .HDR | ESRI BIL Header File |
| .HDRP | HDRtist Pro Document |
| .HDS | Parallels Desktop Hard Disk File |
| .HDT | Photoshop HDR Toning Preset File |
| .HDUMX | HotDocs User Mapping XML File |
| .HDV | High Definition Video Format |
| .HDX | Delphi MultiHelp Index File |
| .HDZ | Compressed Poser Hand Pose File |
| .HE | Humongous Entertainment Game Archive |
| .HE0 | Humongous Entertainment Game Archive |
| .HE1 | Humongous Entertainment Game Archive |
| .HE2 | Humongous Entertainment Game Archive |
| .HE4 | Humongous Entertainment Sound Archive |
| .HEARTSSAVE-MS | Microsoft Hearts Save File |
| .HEIC | High Efficiency Image Format |
| .HEIF | High Efficiency Image Format |
| .HELP | Mac OS X Help Book |
| .HELPCFG | Adobe Community Help Configuration File |
| .HELPINDEX | Help Index Document |
| .HES | Hudson Entertainment Sound Format |
| .HEVC | High Efficiency Video Coding File |
| .HEX | Hexadecimal Source File |
| .HF | HF Image |
| .HFD | HotDocs Form Document |
| .HFP | HitFilm Project |
| .HFS | HFS Disk Image File |
| .HFT | HotDocs Form Template |
| .HFV | HFS Disk Image |
| .HGL | HP Graphics Language File |
| .HGT | SRTM Elevation Data File |
| .HH | C++ Header File |
| .HHC | HTML Help Table of Contents |
| .HHH | Power C Precompiled Header File |
| .HHI | The Sims 4 Household Data File |
| .HHK | HTML Help Index |
| .HHP | HTML Help Workshop Project |
| .HHSL | Hockey High Score List File |
| .HHT | Help and Support Center HHT File |
| .HI | MacMAME High Scores File |
| .HID | KeepSafe File |
| .HID2 | KeepSafe File |
| .HIF | Quicken Online File |
| .HIGHLAND | Highland Document |
| .HIN | HyperChem Input File |
| .HIP | Houdini Project File |
| .HIPNC | Houdini Apprentice File |
| .HIS | FindinSite Database Definition File |
| .HIT | The Sims Sound File |
| .HIV | Windows Registry Hive File |
| .HJT | TreePad 6 Database File |
| .HKDB | Apple iTunes Library File |
| .HKI | WinHKI Archive |
| .HKI1 | WinHKI HKI1 Archive |
| .HKI2 | WinHKI HKI2 Archive |
| .HKI3 | WinHKI HKI3 Archive |
| .HKM | Havok Movie File |
| .HKX | Havok Packed File |
| .HL | HeuristicLab Storage File |
| .HLB | VMS / VAX Help Library |
| .HLP | Windows Help File |
| .HLSL | High Level Shader Language File |
| .HLX | ATI Radeon Video Driver Support File |
| .HM3 | Help & Manual 3 Project |
| .HMA | Sony HI-MD Audio File |
| .HME | Windows Mobile Theme File |
| .HMI | HMI Audio File |
| .HMK | Hallmark Card Studio File |
| .HML | HostMonitor TestList File |
| .HMP | Worms Height Map File |
| .HMS | HostMonitor Script File |
| .HMT | HighMAT File |
| .HMX | Help & Manual 4 Project |
| .HMXP | Help & Manual XML Project |
| .HMXZ | Help & Manual Compressed Project |
| .HOF | OMSI Map Parameter File |
| .HOG | Descent Mission File |
| .HOI4 | Hearts of Iron IV Game Save File |
| .HOL | Outlook Holidays File |
| .HONMOD | HON Modification Manager File |
| .HOT | 4x4 Evolution Hot Lap File |
| .HOW2 | Visma Performit Player Configuration File |
| .HPD | HotDocs PDF Document |
| .HPF | High Performance Fortran File |
| .HPG | HPGL Plot File |
| .HPGL | HP Graphics Language Plotter File |
| .HPI | Hemera Photo Objects Image File |
| .HPJ | Help Project File |
| .HPK | HPack Compressed Archive |
| .HPKG | Haiku Package File |
| .HPL | HP-GL Plotter File |
| .HPP | C++ Header File |
| .HPR | Internal RoboHelp File |
| .HPS | HP Digital Sender Metadata File |
| .HPT | HotDocs PDF Template |
| .HQM | Hardcore Questing Mode Data File |
| .HQX | BinHex 4.0 Encoded File |
| .HR | TRS-80 Image |
| .HR2 | Poser Hair File |
| .HRF | Hitachi Raster Format File |
| .HRL | Erlang Header File |
| .HRZ | Compressed Poser Hair File |
| .HS | Motorola Flash Flex File |
| .HS2 | HyperRESEARCH 2 Study File |
| .HSB | HALion Sound Bank File |
| .HSC | Aspen HYSYS Simulation File |
| .HSDT | Thinkfree Office NEO Show Template |
| .HSF | HOOPS Stream Format File |
| .HSH | Windows Catalog Search Index File |
| .HSK | Huskey Truss & Building Supply Import File |
| .HST | History File |
| .HT | HyperTerminal Session File |
| .HTA | HTML Application |
| .HTACCESS | Apache HTACCESS File |
| .HTB | Audacity Help File |
| .HTC | HTML Component File |
| .HTG | HackTheGame Mission Pack |
| .HTK | Hidden Markov Model Toolkit Audio |
| .HTM | Hypertext Markup Language File |
| .HTML | Hypertext Markup Language File |
| .HTML0 | Book Designer File |
| .HTMLZ | Zipped HTML eBook |
| .HTMOD | Hardware Tycoon Game Mod File |
| .HTPASSWD | Apache HTACCESS File |
| .HTT | Hypertext Template File |
| .HTX | HTML Extension File |
| .HTXT | Hanvon eBook File |
| .HTZ4 | HyperMaker 4 Publication |
| .HTZ5 | HyperMaker 5 Publication |
| .HUH | HydroCAD Unit Hydrograph Definitions File |
| .HUM | OMSI Human Configuration File |
| .HUS | Husqvarna Embroidery File |
| .HVC | HotDocs Variable Collection File |
| .HVE | Windows Registry Hive File |
| .HVIF | Haiku Vector Icon File |
| .HVPL | iTunes Visual Plug-in File |
| .HWD | Hedgewars Demo File |
| .HWDT | Thinkfree Office NEO Word Template |
| .HWMAP | Hedgewars Drawn Map File |
| .HWP | Hangul (Korean) Text Document |
| .HWS | Hedgewars Saved Game |
| .HX | Haxe Source Code Module |
| .HXA | Microsoft Help 2 Attribute Definition File |
| .HXC | Microsoft Help 2 Collection Definition File |
| .HXE | Microsoft Help 2 Sample Definition File |
| .HXK | Microsoft Help 2 Index File |
| .HXM | Descent 2 Resource Modification |
| .HXN | Hexagon Model File |
| .HXS | Help 2 Compiled Help File |
| .HXT | Microsoft Help 2 Table of Contents File |
| .HXX | C++ Source Code Header File |
| .HYDRA | Hydra Image Filter Program File |
| .HYP | Dictionary Information File |
| .HYPE | Hype Document |
| .HYPERESOURCES | Hype Resources Folder |
| .HYPESYMBOL | Hype Symbol File |
| .HYPETEMPLATE | Hype Document Template |
| .HYV | Team Manager Meet Event File |
| .HZ | Chinese (Hanzi) Text |