Download the file and make sure you save it in "UNIX" format, not DOS (i.e. newline delimited not the nasty <CR><LF> cruft) -- (if you are not sure how to do that running the dos2unix(1) command will assure it's was not unix format when you are done).
% file awkdoc
awkdoc: troff or preprocessor input text, ASCII text
% man groff
We'll leave it to you to figure out which switches for troff/groff and macro package (hint: try the head(1) command to peak at the first few lines -- there are three likely choices, but it's pretty obvious since the same one as most V7 documents).
FWIW: If you got a copy of Kernighan and Pike's - "The Unix Programming Environment" [ISBN 0-13-937699-2] which is available at most retailers. You can read Chapter 9 for this question. Although, given so many of the questions you seem to like to ask here, please consider doing all the exercises in the entire book.