What is the MDI file format?
.mdi files are generated and managed by the Microsoft Office Document Imaging (MODI) utility, available in Microsoft Office XP, 2003 and 2007. MODI was discontinued after Office 2010 and is no longer bundled with current Office or Windows releases. An .mdi file is a high-resolution graphic file containing scanned documents, stored as a proprietary multi-page raster image.
.mdi files are tag-based, which enables their use with optical character recognition (OCR) software. Graphical data in an .mdi file can be converted into a plain text file and saved as a Microsoft Word .DOC document.
.mdi files can be converted into TIFF format for better compatibility with third-party software. Despite many structural similarities with TIFF, the .mdi format is proprietary to Microsoft - it uses a modified file header (45 50 2A 00) instead of the standard TIFF signature, which causes regular TIFF viewers to reject it. The official command-line tool mdi2tif.exe (Microsoft MDI to TIFF File Converter) handles this conversion. Saving .mdi files in TIFF format guarantees image compatibility with other programs and applications.
Security & safety
RISK: LOWAn .mdi is a scanned-image data file, not executable, so the file itself is low risk. The main cautions are practical: MDI is obsolete, so migrate important scans to TIFF/PDF now while the free converter still exists. Avoid uploading sensitive scanned documents (IDs, contracts, medical records) to unknown online MDI converters - use Microsoft's offline mdi2tif tool instead. Only download the converter and Office from official Microsoft sources, not third-party "MDI viewer" sites that may bundle adware.
Format details
in a nutshell- Multiple Document Interface (programming term) - "MDI" as a phrase means a windowing style in Windows apps - unrelated to the file format; not a file you open.
- Musical Instrument Digital Interface mis-type - Occasionally confused with MIDI; the music format is .mid/.midi, not .mdi.
Programs that open MDI files
Windows3 apps
Microsoft MDI to TIFF File Converter (mdi2tif)
Free Install it, then run 'MODIfilesNamemdi2tif.exe -source file.mdi -dest file.tif' (or batch a folder) to convert MDI to standard TIFF you can open in Photos. Microsoft's official free tool.
Microsoft Office 2007 (with MODI component)
Paid If you still have Office 2003/2007, double-click the .mdi to open in Microsoft Office Document Imaging (you may need to add the MODI feature). The only app that opens MDI natively with OCR.
Any TIFF/image viewer (after conversion)
Free Once the .mdi is converted to TIFF (above), open the .tif in Windows Photos, IrfanView, or GIMP and print/save to PDF. Technical details
deep spec| Developer | Microsoft Corporation |
| MIME type | image/vnd.ms-modi |
| Magic bytes | 45 50 2A 00 - Microsoft-specific MODI signature, replacing the standard TIFF magic (49 49 2A 00) and causing incompatibility with standard TIFF readers |
| Byte order | Little-endian (Intel byte order), matching TIFF's II-type variant |
| Multi-page support | A single .mdi file stores multiple scanned pages as separate image strips within one container |
| OCR text layer | Embeds recognized text alongside raster image data, generated by MODI's built-in OCR engine |
| B&W compression | CCITT Group 4 (G4) fax compression for black-and-white scanned pages |
| Color/grayscale compression | JPEG compression for color and grayscale page content |
| Tag structure | TIFF-style Image File Directory (IFD) tags with Microsoft-proprietary extension tags |
| Typical scan resolution | 150-300 DPI for standard scanned office documents |
| Viewer compatibility | Rejected by standard TIFF viewers due to modified magic bytes; direct opening requires MODI or conversion to .tif |
| Conversion tool | mdi2tif.exe - official Microsoft MDI to TIFF File Converter, available as a standalone redistributable |
| Discontinuation | MODI was removed from Microsoft Office after Office 2010; .mdi has no native support in current Windows or Office versions |
| Structural basis | Derived from the TIFF specification but incompatible with it due to the altered file signature and proprietary tag extensions |
| Released | Office XP / Office 2003 (Microsoft Office Document Imaging tool) |
| Specification | learn.microsoft.com |
MDI conversions
Community Q&A
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