Compare a single page of two PDF files.

diff-all.sh

#!/bin/bash

FILE_A=$1
FILE_B=$2

PAGE_COUNT_A=$(pdfinfo $FILE_A | grep Pages | awk '{print $2}')
PAGE_COUNT_B=$(pdfinfo $FILE_B | grep Pages | awk '{print $2}')

if [ $PAGE_COUNT_A -eq $PAGE_COUNT_B ];
	then
		for i in $(seq 0 $PAGE_COUNT_A); do
			echo Comparing page $i
	
			convert -density 300 $FILE_A[$i] -transparent white -colorspace RGB -alpha extract -threshold 0 -fill red +opaque black -transparent black A.png
			convert -density 300 $FILE_B[$i] -transparent white -colorspace RGB -alpha extract -threshold 0 -fill blue +opaque black -transparent black B.png
		
			composite -blend 50 A.png B.png diff_$i.png
			rm A.png B.png
		done
	else
		echo Page count of the documents does not match.
		exit 1
fi

diff.sh

#!/bin/bash

FILE_A=$1
FILE_B=$2

convert -density 300 $FILE_A -transparent white -colorspace RGB -alpha extract -threshold 0 -fill red +opaque black -transparent black A.png
convert -density 300 $FILE_B -transparent white -colorspace RGB -alpha extract -threshold 0 -fill blue +opaque black -transparent black B.png

composite -blend 50 A.png B.png diff.png
rm A.png B.png