Windows does not generate thumbnail previews for .NEF (Nikon RAW image) file type by default. Also, the Windows Photo Viewer or Windows Live Photo Gallery can’t open .NEF files due to no native support.
By installing a Codec from Nikon, you can add thumbnail and preview support for .NEF files in Windows.
Nikon RAW Codec is a software module that enables you to handle RAW image files (*.NEF: Nikon Electronic Format) under Microsoft® Windows 8 and Windows 10 with the same ease as JPEG or TIFF images. After installing the Nikon RAW Codec, Windows will be able to view thumbnail preview for .NEF file types in Explorer.
Download Nikon RAW Codec from Nikon’s Website.
32- and 64-bit editions of: Windows 10 Home, Windows 10 Pro, and Windows 10 Enterprise Windows 8.1, Windows 8.1 Pro, and Windows 8.1 Enterprise
Windows Photo Gallery, Windows Live Photo Gallery, and Windows Photo Viewer now display the previews embedded in NEF (RAW) images.