The actual `man` command does this:
/usr/bin/tbl | /usr/bin/groff -Wall -mtty-char -Tascii -mandoc -c | /usr/bin/less -is
So you could do it "manually" that way. Not the cleanest or prettiest solution but it's much lighter weight than using something like pandoc.
EDIT: Full example:
{ /usr/bin/tbl | /usr/bin/groff -Wall -mtty-char -Tascii -mandoc -c | /usr/bin/less -is; } <<EOF
.\" Manpage for encpass.sh.
.\" Email contact@plyint.com to correct errors or typos.
.TH man 8 "06 March 2020" "1.0" "encpass.sh man page"
.SH NAME
encpass.sh \- Use encrypted passwords in shell scripts
...
EOF
