This camera requires at least LR 6.1, so you either have to upgrade (79 US Dollars or equivalent), or use the free DNG converter to convert your NEF files to DNG files that can be read by LR5.
What Per Berntsen said.
Nikon D810A, NEF files are not recognized, but NEF files from a D810 are recognized. The firmware on both cameras is 1.01.
So you're aware, Raw file formats are unique to each camera make and model. NEFs are different for each Nikon camera model. Firmware updates rarely affect the Raw file format. Sometimes, but rarely.
Camera models supported by Adobe and the version of Lightroom required are listed here.
D810 - first supported in Lightroom 5.6
D810A - first supported in Lightroom 6.1
Support for new cameras is never retrospectively added to older versions of Lightroom.
thanks, I did download the converter and that works, now trying to find out how to get the upgrade.