Notes about the 21W file extension:
To open this file type, a required software must be installed. Without it you only see a Windows message "The following file cannot be opened
" (Windows 7) or "How do you want to open this file?
" (Windows 10) if you double-click the file. There click on "More apps"
and choose a suitable software to view such files on your PC or from email attachments.
The 21W file type is primarily associated with 'Snood' by David Dobson. Generally found as the file SNOODPRF.21W.
Detailed information for file extension 21W:
Primary association: Snood
File classification: Game
To change file associations press Windows Key
and then Apps and Features
> Default apps
> Choose default apps by file type
Invalid file associations could be the result of underlying issues within your Windows PC.