Notes about the RTFD 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 RTFD file type is primarily associated with 'NeXT RTF-Packet' by Apple Inc.. This is a Rich Text File with Attachments (usually pictures). NeXT returned the format to Apple in 1996. It is in the format of a directory, with an .RTF inside, along with the images. Use TextEdit on Mac OS X to open these files on a Macintosh computer.