ADU File

What are ADU files and how to open them

Are you having problems opening an ADU file or are you simply curious about its contents? We're here to explain the properties of these files and provide you with software that can open or handle your ADU files.

What is an ADU file?

An .ADU file is an Addict User Dictionary file.

The Addict User Dictionary stores custom vocabulary used by the Addict spell-checking component from Addictive Software. It holds a list of words the user has added so they are recognised by Addict's spell checker and thesaurus, rather than flagged as misspellings. These files help preserve user-defined words across documents and sessions under Windows, especially when Addict is used with development tools like Delphi or C++Builder.

Addict generates .ADU files when the user accepts or adds words via its spell-checking or autocorrect features. Later, the component reads the file to know which terms are valid in the user's custom dictionary. Because Addict is discontinued, many users convert .ADU files into simpler formats (such as TXT, DIC or CSV) so their custom dictionary can be used with more modern or open-source tools.

The file's contents begin with a header in ASCII text: "Addict User Dictionary, Version " starting at offset 0 (that is, the bytes 0x41646469637420557365722044696374696F6E6172792C2056657273696F6E20), followed by a period at offset 33. After that header, the file includes the list of user-added terms (one per line or other internal structure) that Addict matches against.

How to open ADU files

Important: Different programs may use files with the ADU file extension for different purposes, so unless you are sure which format your ADU file is, you may need to try a few different programs.

While we have not verified the apps ourselves yet, our users have suggested two different ADU openers which you will find listed below.

Last updated: August 17, 2026

Various apps that use files with this extension

These apps are known to open certain types of ADU files. Remember, different programs may use ADU files for different purposes, so you may need to try out a few of them to be able to open your specific file.

Help us help others

File.org helps thousands of users every day, and we would love to hear from you if you have additional information about ADU file formats, example files, or compatible programs. Please use the links below or email us at submit@file.org to discuss further.