How to read a .man file not on manpath?

You can try to read your file by doing

man path_to_file

as man will treat the given argument as a file if it finds a slash / in it. For instance

man ./my_test

will open the my_test file, while

man my_test

will look in the standard manual for the given command.

If your man page is in a non-standard directory location, you can use:

man -M <path to man directory> mymanpage

You can also use the MANPATH environment variable:

MANPATH=<path to man directory> man mymanpage

If you are looking to format a standalone man page, use nroff:

nroff -man mymanpage.1

The option -l, --local-file, as documented in man man

man -l ./doc/mypage.1