Autocompile and display a Groff document

autocompile.sh

/bin/sh
# Automatically compiles and views a pdf from Groff. [Requires Zathura, entr]

if [ $# -eq 0 ] || [ "$1" == "-h" ] ; then
    echo "Usage: \$0 \$1"
    echo "  \$0     The name of the ms document you wish to autocompile."
    echo "  \$1     The name of the output."
    exit
fi

[ -f $2 ] || touch $2


echo "Autocompiling and displaying $1!"
echo "$1" | entr sh -c 'refer references.bib "$1" | groff -ms "$1" -Tpdf > "$2"' . "$1" "$2" &
zathura $2

This command works fine but I get the following errors from Zathura (mupdf):

error: cannot recognize version marker
warning: trying to repair broken xref
warning: repairing PDF document
error: cannot tell in file
error: could not open document 

Can anyone help?