This works to concatenate PDFs

gistfile1.rb

# This class uses the pdftk toolkit.

class PdfToolkit

  # Merges some pdf files to output file
  #
  # options
  #   :from_files - array of source pdf files
  #   :to_file    - output file
  #
  def self.merge(options)
    command = "\"#{options[:from_files].join('" "')}\" cat output \"#{options[:to_file]}\""
    run(command)
  end

  # Fills pdf data in pdf form and creates output file
  #
  # options
  #   :form_file  - pattern file
  #   :data_file  - file with form data
  #   :to_file    - output file
  #   :flatten    - if true then document will be made readonly after filling
  def self.fill_form(options)
    command = "\"#{options[:form_file]}\" fill_form \"#{options[:data_file]}\" output \"#{options[:to_file]}\" #{"flatten" if options[:flatten]}"
    run(command)
  end

  private

  # Runs pdftk util.
  def self.run(command)
    full_command = "pdftk #{command}"
    output = %x[ #{full_command} ]
    return_status = $?

    if return_status.nil? or return_status.success? != true
      raise "Running PDFTK tool failed with: #{full_command} / #{output}"
    end

  end

end