Watermark in existing PDF in Ruby

Question

I would like to add a dynamically generated text. Is there a way to watermark an existing PDF in Ruby?

Answer 1

This will do it:

PDF::Reader to count the number of pages in the file.

Prawn to create a new PDF document using each page of the input pdf as a template.

require 'prawn'
require 'pdf-reader'

input_filename = 'input.pdf'
output_filename = 'output.pdf'

page_count = PDF::Reader.new(input_filename).page_count

Prawn::Document.generate(output_filename, :skip_page_creation => true) do |pdf|

  page_count.times do |num|
    pdf.start_new_page(:template => input_filename, :template_page => num+1)
    pdf.text('WATERMARK')
  end

end

However, in my testing the output file size was huge with the latest Gem version of Prawn (0.12), but after pointing my Gemfile at the master branch on github, all worked fine.