#!/bin/bash

# Create the destination file and temporary files

file=original53.pdf;

newfile=$(basename $file .pdf)-2.pdf;

tmpfile=$(mktemp --suffix=.pdf);

blankfile=$(mktemp --suffix=.pdf);

cp -f $file $newfile;

cp -f $file $tmpfile;

# Find the number of pages

numberofpages=`pdftk $file dump_data | grep "NumberOfPages" | sed 's:.*\([0-9][0-9*]\).*:\1:'`;

# Insert blank pages until the number of pages is a multiple of 4

echo "" | ps2pdf -sPAPERSIZE=a4 - $blankfile;

while (( $numberofpages % 4 != 0 )); # DIFFERENCE: %% instead of % since % is used by Nautilus-Actions for special parameters

do 

  ((numberofpages++));

  pdftk A=$newfile B=$blankfile cat A B output $tmpfile;

  cp -f $tmpfile $newfile;

done;

# Reorder every 4 pages of a PDF following the permutation 1234 -> 1342

a=0;

neworder=$(

  while [ $a -lt $numberofpages ];

  do 

    echo -n "$(($a + 1)) $(($a + 3)) $(($a + 4)) $(($a + 2)) ";

    ((a+=4));

  done;

);

pdftk $tmpfile cat $neworder output $newfile;