pdf_add_blanks.rb

#!/usr/bin/env ruby
# encoding: utf-8

f = ARGV[0] || exit(1)

# get page count
n = `pdfinfo #{f} | grep Pages | cut -d":" -f2`.strip.to_i

# create empty page
`cd /tmp && convert -page A4 xc:white __blankpage.pdf`

# build pdftk command
cmd = "pdftk A=#{f} B=/tmp/__blankpage.pdf cat  "

cmd << (0...n).map{|i| "A#{i+1} " }.join("B1 ")
cmd << " output #{f.chomp(".pdf")}_with_blanks.pdf"

puts cmd
system(cmd)