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The File Extension Library

What is a file extension?

Short answer: it's the set of letters after the period (.) in the name of a file.

Long answer: File extensions signify the file format of a file. It tells the operating system (OS) how data was stored in the file. Not all OS, require a file extension though. For instance, this is optional in Unix, but is mandatory with MS-DOS and Windows systems.

In most file formats the file type is actually defined by the contents (first bytes, file structure), but extensions are used to define the application that is used for opening the file.

Below is a detailed database of thousands of file extensions our team has compiled for you. Feel free to browse!


Browse all Extensions:
ABCDEFGHIJKLMNOPQRSTUVWXYZ
HHK - Extension Details
Date Added: January 01, 1970
File Extension:  .HHK
Description 1: .HHK file extension is linked with HTML Help Index. This is the index of files that can be accessed by Microsoft HTML Help which is a webbased help interface. .HHK file extension is also associated with Microsoft Windows a popular Operating System from Microsoft Corporation. Windows and other Microsoft operating systems can run on various platforms such as: PCs, servers and embedded devices.
File Type:   System File
Mode: Binary
Program(s) to Open:  Windows: HTML Help Workshop
Common:
Extension: