I understand LR 4.4 will not read the Nikon D810 RAW files. however, I see several plugins for various Adobe products.
I could not figure out which plugin I can install, if any?
Lightroom does not use plugins (Adobe Camera Raw) to read Raw files. It has its own Raw engine built in.
The Nikon D810 was first supported in Lightroom 5.6.
Support for newer cameras is never added retrospectively to older versions of the software so you'll never be able to open Raw D810 files in LR 4.4.