You install a codec that teaches Windows 7 how to "read" the NEF file.
If you want and a simple interface: Go with FastStone .
Older versions of this codec may not support the newest Nikon Z-series or D850 files. 2. Nikon NX Studio (The Official Choice) nef file viewer windows 7 free download
The most seamless way to view NEF files on Windows 7 is to enable "thumbnail" support in Windows Explorer. By default, Windows 7 cannot read Nikon’s proprietary RAW format.
Allows you to see thumbnails in your folders and open images directly in the built-in Windows Photo Viewer . You install a codec that teaches Windows 7
Extremely low RAM usage; works perfectly on older Windows 7 machines with limited power. 5. DigiKam (The Pro-Level Organizer)
Which of these sounds like the best fit for your ? Allows you to see thumbnails in your folders
Nikon offers its own proprietary software for free. While the latest versions are optimized for Windows 10 and 11, you can still find legacy versions of or Capture NX-D that are fully compatible with Windows 7.