When I was unable to open up a .mdi file that I just saved, I had to find the fix. I already knew that I had installed the feature (Microsoft Document Image Writer) correctly, but I double checked that.
When the newly saved “mdi” file wouldn’t open in WORD or Internet Explorer, I back tracked and found the little nugget that runs that command.
Search for MSPVIEW.exe in your Programs folder. I actually found mine in C:\Program Files\Common Files\Microsoft Shared\MODI\11.0.
Ok, now right click on your mdi file, choose OPEN WITH, CHOOSE PROGRAM… and browse to the folder where the MSPVIEW.exe is located. Double click on it to select it, click OK and your file will open. However, to make it ALWAYS open with the document viewer, right click on your file again, select OPEN WITH, CHOOSE PROGRAM… and now this time the Microsoft Document Image Writer is a listed program. Click on it to select it and then put a check in the box next to Always use the selected program to open this kind of file, click OK and shazam! Good to go!