diff of multipage pdfs using imagemagick and pdftk

pdfdiff.sh

#!/bin/bash

# visual diff of two pdfs
#
# inspired by:
# http://usakuv.blogspot.fr/2011/05/visual-diff-for-pdf-files.html
# https://docs.google.com/document/pub?id=10GBd9u4e-NwNCd-4t4hb9rcdKJlFFhkkq-b_ezzg73c

print_help() {
        echo "Usage: $0 a.pdf b.pdf diff.pdf" >&2
}

baseWD=`date +%s`"diff-PDF-work-dir"
WD="$PWD/$baseWD"

if [ $# = 3 ]; then
    if [ -f "$1" -a -r "$1" -a -f "$2" -a -r "$2" -a -w "$PWD" ]; then
        if mkdir "$WD"; then
            ln -s `readlink -f "$1"` "$WD/1.pdf"
            ln -s `readlink -f "$2"` "$WD/2.pdf"
            pushd "$WD" >/dev/null
            pdftk 1.pdf burst output a%08d.pdf
            rm doc_data.txt
            pdftk 2.pdf burst output b%08d.pdf
            rm doc_data.txt
            if [ -e a00000001.pdf ]; then
                for aFile in a????????.pdf; do
                    bFile=`echo $aFile | sed 's/a/b/'`
                    cFile=`echo $aFile | sed 's/a/c/'`
                    if [ -e $bFile ]; then
                        compare $aFile $bFile $cFile
                    fi
                done
                pdftk c????????.pdf cat output 3.pdf
            fi
            popd >/dev/null
            mv "$WD/3.pdf" "$3"
            rm -rf "$WD"
        else
            echo "Could not create the working directory $baseWD." >&2
            exit 3;
        fi
    else
        echo "Permission error." >&2
        exit 2;
    fi
else
    print_help;
    exit 1;
fi