How to produce an A4-format pdf of an man page?
Right now you are running groff twice, once as part of man -t, once on it‘s own on the PostScript file generated by man.

Try

groff -Tps -mandoc -c -P-pa4 /usr/share/man/man1/ls.1 &gt;out.ps
ps2pdf out.ps man-ls.pdf
open man-ls.pdf


or directly

groff -Tps -mandoc -c -P-pa4 /usr/share/man/man1/ls.1 | 
    open -f -a /Applications/Preview.app




To have it work for all man pages accessible to man, a little script will help. 

#!/bin/sh
page=$(man -W $1)
if [ -r "$page" ]; then
    groff -Tps -mandoc -c -P-pa4 "$page" | open -f -a Preview.app
fi


Save it as manA4, run chmod +x manA4 once, and then use it as manA4 ls. 



In case you are working with compressed man pages (which macOS does not use by default) you need to uncompress them on the fly.

#!/bin/bash
page=$(man -W $1)
if [ -r "$page" ]; then
    if [[ "$page" =~ .*.gz$ ]]; then
        gzcat "$page" | groff -Tps -mandoc -c -P-pa4 | open -f -a Preview.app
    else
        groff -Tps -mandoc -c -P-pa4 "$page" | open -f -a Preview.app
    fi
fi