Notes about the DDX 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 DDX file type is primarily associated with 'Alpha Five' by Alpha Software, Inc.. Contains the dictionary's index(es). Alpha Five uses the .ddx to find a specific form name or field rule or whatever is needed.