Cannot open .mdi file in Office 2003

[Johnc72]

I have Office 2003. I cannot open .mdi files. When I click the file I get
the window "Windows cannot open this file" with a choice to go to the web or
choose an application.
When I choose Open With, I see "Microsoft Office Document Imaging" but I get
the
error message "The selected file is not a valid Microsoft Office
Document Imaging file."
However, I think the file is valid because people who received the same file
said they could open it. Any help?