A bash script to crop out the margins of the PDF file.

croppdf.sh

#!/bin/bash
INPUT=${1:?}
OUTPUT=${2:-${INPUT//.pdf/-crop.pdf}}

get_bbox() {
  gs -sDEVICE=bbox \
     -dBATCH -dNOPAUSE \
     -c save pop \
     -f ${INPUT} 2>&1 \
  | grep 'HiResBoundingBox' \
  | awk 'BEGIN{x0=9999;y0=9999;} {x0=(x0<$2)?x0:$2;y0=(y0<$3)?y0:$3;W=(W>$4)?W:$4;H=(H>$5)?H:$5;} END {printf "%.6f %.6f %.6f %.6f", x0, y0, W, H}'
}

BBOX=$(get_bbox)

gs -o ${OUTPUT} \
   -sDEVICE=pdfwrite \
   -c "[/CropBox [${BBOX}]" \
   -c "/PAGES pdfmark" \
   -f ${INPUT}

echo "## intput file: ${INPUT}"
pdfinfo ${INPUT}
echo ""

echo "## output file: ${OUTPUT}"
pdfinfo ${OUTPUT}