NEF is a format for original, raw graphic files created by Nikon technology. Accordingly, the developer of the format is also the specified company. The name of the format is an abbreviation for Nikon Electronic Format. At the same time, NEF format files received by Nikon cameras of different models can have a different structure, so compatibility is not guaranteed. Nikon's graphic editors are geared towards supporting specific camera models. When creating a file, the data comes directly from the matrix. NEF files are of good quality and contain metadata, and therefore take up a lot of space.
PDF is short for Portable Document Format, which can be translated from English as “Portable Document Format”. It was developed by Adobe Systems for use by US federal authorities as a tool for storing working documents. This is a universal cross-platform format, which is now standard for electronic documents. It serves to convert text files (including photographs or other images) into electronic documents without any loss. To read PDF files you need special programs - Adobe (Acrobat) Reader, PDF-Viewer and others.