Thanks for sharing your groff file. I'm on a Debian derivative and running the below command did produce a pdf but the line "This paragraph should be right-justified and indented by th" was chopped off on the right side:
groff -Tpdf example.groff > example.pdf
Also, the left/right margins are partically non-existent (top/bottom margins look fine).
Did I miss any command-line option?