MDI files are Microsoft Document Imaging files. This file type is most common for scanned files or for saving files within Microsoft Office that need to be printed at a time when a printer is not accessible. Similar to a PDF, an MDI file preserves document formatting better than a DOC file, although a PDF is more universally accessible. Microsoft Office is needed to open an MDI file, while a PDF can be opened with a number of free programs. Converting an MDI into a PDF is a quick and easy process.
Load Microsoft Word.
Click "File," then "Open" and locate the MDI file you wish to save in PDF format. Click once on the file name to highlight it, then click the "Open" button.
Click "File," then "Save As." Name your document something unique and select "PDF (*.pdf)" from the "Save as Type" drop-down menu. (If you don't have this option, you'll need to install the free Microsoft Office Save As PDF Add-in.) Click "Save." Your document should now be in PDF format.