Here are the complete 1988-vintage Sun manuals “Using NROFF and TROFF†and “Formatting Documents†scanned just for you. I’d scanned these in 2000, and they’d sat on a forgotten archive volume since then.
Update: there are better versions on the Internet Archive: Using NROFF and TROFF and Formatting Documents, all as part of the Sun Microsystems, Inc. manual collection.
(if you need to get your troff on, go to Ralph’s troff.org.)