pdf_downsample.sh

#!/bin/bash
#
#  Script for converting PDF documents. It tries to get rid of active content
#  as well as potential exploits in images without substantial loss of quality.
#

set -e

DPI=72

if [[ $# -lt 1 ]]; then
    echo "USAGE $0 <filename1.pdf> [filename2.pdf] ..."
    exit 0
fi

for file in "$@"; do

    if [[ ! -r ${file} ]]; then
        echo "File ${file} is not readable."
        exit -1
    fi

    echo "[+] Creating downsampled PDF for ${file} ..."

    gs  -dBATCH -dNOPAUSE -dQUIET -dSAFER \
        -sDEVICE=pdfwrite \
        -sOutputFile=output.pdf \
        -dDownsampleColorImages=true \
        -dColorImageResolution=150 \
        -dDownsampleGrayImages=true \
        -dColorImageDownsampleThreshold=1 \
        -dGrayImageDownsampleThreshold=1 \
        -dColorImageDownsampleType=/Bicubic \
        -dGrayImageDownsampleType=/Bicubic \
        -dColorImageResolution=${DPI} \
        -dGrayImageResolution=${DPI} \
        -dMonoImageResolution=100 ${file}

    echo "[+] Moving old file ${file} to old_${file}"

    mv ${file} old_${file} && mv output.pdf ${file}

done