This article explains what THEMEPACK files are and how to use them in Windows.
ThemePack App – Full Review and How to Use
A file with the THEMEPACK file extension is a Windows theme pack file. They are created by Windows 7 to apply similar theme backgrounds, window colors, sounds, icons, cursors, and screensavers.
THEMEPACK files can be opened in Windows 11, 10, and 8, just like in Windows 7. You can do this by simply double-clicking or double-tapping the file. No other program or installation utility is needed to run the files.
The newer .DESKTHEMEPACK files are not backwards compatible with Windows 7. This means that while .THEMEPACK files can be opened in all four versions of Windows, they will only open in Windows 11, 10, and 8.