FWIW, .rd does work in Ubuntu 20.04 -Jim
$ echo ".rd" >/tmp/test.tr ; groff -Tascii /tmp/test.tr | cat -s foo bar [^D] foo bar
FWIW, .rd does work in Ubuntu 20.04 -Jim
$ echo ".rd" >/tmp/test.tr ; groff -Tascii /tmp/test.tr | cat -s foo bar [^D] foo bar