doc.tr is the updated source file for the nroff/troff User's Manual,
with the new paragraphing features and various corrections.

troffdoc.pdf was built directly from the source file (February 22, 2019 version).

troffdoc-an.pdf is highlighted to show the differences between the
February 22 and January 27 versions.

troffdoc-20190127.pdf is the January 27, 2019 version.

troffdoc-20190127-mk-an.pdf is the January 27 version with the changed lines
flagged with gdiffmk.  Additionally, changes have been highlighted so they
are easier to find.

changes.pdf provides a detailed description of the document changes for the
January 27 and February 22 versions.