| .H | The Eclipse Foundation | Developer Files | C/C++/Objective-C Header File | MacroMates TextMate | MacroMates |
| .HAC | Open Source | Developer Files | Helma Actions Script | Helma | Open Source |
| .HAML | Sublime HQ Pty Ltd | Developer Files | HTML Abstraction Markup Language File | Microsoft Notepad | Microsoft Corporation |
| .HAY | Open Source | Developer Files | Haydee Web Server Module Content File | Notepad++ | Don Ho |
| .HBS | GitHub, Inc. | Developer Files | Handlebars Template | Handlebars | GitHub, Inc. |
| .HBX | Open Source | Developer Files | BinHex Encoded File | Smith Micro StuffIt Deluxe | Smith Micro Software |
| .HC | Open Source | Developer Files | VeraCrypt Container File | VeraCrypt | Open Source |
| .HCF | Zaplots Games, Inc. | Developer Files | Compact Ham Library | Zaplots HAM Runtime | Zaplots Games, Inc. |
| .HEX | Intel Corporation | Developer Files | Hexadecimal Source File | Heaventools FlexHex | Heaventools Software |
| .HH | Microsoft Corporation | Developer Files | C++ Header File | Microsoft Notepad | Microsoft Corporation |
| .HHH | Mix Software | Developer Files | Power C Precompiled Header File | Power C Compiler | Mix Software |
| .HHP | Microsoft Corporation | Developer Files | HTML Help Workshop Project | Microsoft HTML Help Workshop | Microsoft Corporation |
| .HISTORY | The Eclipse Foundation | Developer Files | Eclipse IDE Local History Data | Eclipse IDE for Java Developers | The Eclipse Foundation |
| .HM | Microsoft Corporation | Developer Files | Windows Help Context IDs | Microsoft Visual C++ | Microsoft Corporation |
| .HMF | Tech Soft 3D | Developer Files | HOOPS Metafile | HOOPS | Tech Soft 3D |
| .HOC | Open Source | Developer Files | High Order Calculator (HOC) Script File | High Order Calculator (HOC) | Open Source |
| .HPF | IBM | Developer Files | High Performance Fortran File | Microsoft Notepad | Microsoft Corporation |
| .HPP | Microsoft Corporation | Developer Files | C++ Header File | Microsoft Notepad | Microsoft Corporation |
| .HRL | Ericsson Computer Science Laboratory | Developer Files | Erlang Header File | Microsoft Notepad | Microsoft Corporation |
| .HS | Open Source | Developer Files | Haskell Script | MacroMates TextMate | MacroMates |
| .HSC | Aspen Technology, Inc. | Developer Files | Aspen HYSYS Simulation File | Aspen HYSYS | Aspen Technology, Inc. |
| .HSE | Adobe Systems Incorporated | Developer Files | Homesite Snippet End | Adobe Dreamweaver | Adobe Systems Incorporated |
| .HSM | Unknown Developer | Developer Files | Assembly Language Header File | Assembly Programming Language | Unknown Developer |
| .HSP | HeliumScraper.com | Developer Files | Helium Scraper Project File | Helium Scraper | HeliumScraper.com |
| .HTML5 | Sublime HQ Pty Ltd | Developer Files | HTML5 Hypertext Markup Language Revision 5 Source Code | Microsoft Notepad | Microsoft Corporation |
| .HTR | Microsoft Corporation | Developer Files | Microsoft Windows NT Password Services Script | Windows NT | Microsoft Corporation |
| .HWPROJ | Microsoft Corporation | Developer Files | Visual Studio .NET Help Project | Microsoft Visual Basic | Microsoft Corporation |
| .HX | Thermo Fisher Scientific Inc. | Developer Files | Amira 3D Mesh File | Amira | Thermo Fisher Scientific Inc. |
| .HXML | Open Source | Developer Files | HaXe Make File | Haxe | Open Source |
| .HXX | The Qt Company | Developer Files | C++ Source Code Header File | MacroMates TextMate | MacroMates |
| .HZP | Rowley Associates Ltd | Developer Files | CrossWorks For ARM Project | CrossWorks for ARM | Rowley Associates Ltd |
| .H__ | Microsoft Corporation | Developer Files | C++ Header File | Microsoft Notepad | Microsoft Corporation |
of 1 
