This is just the intro. The full document is available at https://archive.org/details/a_research_unix_reader/ .
Sending a message to hn@yc to try and get the link changed.
some people at cat-v.org were interested in this and there happened to be a copy at stanford library where a roommate of mine was working at the time. he borrowed it on my behalf and i used the book scanner at noisebridge in san francisco (constructed from wood and two canon cameras and a python script) to image it, and uploaded it to archive.org.