You're here because you have a file that has a file extension ending in .adu. Files with the file extension .adu can only be launched by certain applications. It's possible that .adu files are data files rather than documents or media, which means they're not meant to be viewed at all.

Files stored in the ADU format are used by an application that can be added to word processing software or to text editing applications developed for Microsoft Windows-based systems. These ADU files are classified as data files because stored in a file with the .adu extension includes pieces of data which can be referenced by a word processing software or a text editor that has been added with the main application that is used to create, open and edit these ADU files. These ADU files are also called Addict user dictionary files due to the nature of the content of a file stored in the .adu format. The Addict software can be used to create, open and edit the content of an ADU file. Addictive Software developed the Addict software as an application which can be added to widely used word processing and text editing programs like Microsoft Word, Microsoft WordPad and Microsoft Notepad among others. This application can be installed by users of computers running on Microsoft Windows systems, so they can create and open these ADU files. The content of these ADU files include dictionary terms that can be referenced by the associated word processing or text editing software added with the Addict software, and this happens when the user accesses the grammar and spell checking features integrated into the word processing or text editor application. Files with the .adu extension are also used as reference data files when a user accesses the thesaurus features implemented into the associated word processing or text editor software.

Launch a .adu file, or any other file on your PC, by double-clicking it. If your file associations are set up correctly, the application that's meant to open your .adu file will open it. It's possible you may need to download or purchase the correct application. It's also possible that you have the correct application on your PC, but .adu files aren't yet associated with it. In this case, when you try to open a .adu file, you can tell Windows which application is the correct one for that file. From then on, opening a  .adu file will open the correct application. Click here to fix .adu file association errors

Be careful not to rename the extension on .adu files, or any other files. This will not change the file type. Only special conversion software can change a file from one file type to another.

A file extension is the set of three or four characters at the end of a filename; in this case, .adu. File extensions tell you what type of file it is, and tell Windows what programs can open it. Windows often associates a default program to each file extension, so that when you double-click the file, the program launches automatically. When that program is no longer on your PC, you can sometimes get an error when you try to open the associated file.