For those unclear on what the large pile of .doc and .pdf files are, it appears to be some revision of the design documents for "NT OS/2", which then turned into just NT. This appears to be the Smithsonian description of their physical copy: https://www.si.edu/object/microsoft-windows-nt-os2-design-wo...

I think this is the only place that hosts a (hopefully) full electronic copy of the book.