gistfile1.txt

require 'prawn'
require 'pdf/toolkit'
  
  class PdfFiller
    DOWNLOAD = "/tmp/downloads"
    FINAL_DIR = "#{Dir.home}/edited_files"

    attr_reader :file_path

    def initialize( file_path)
      @file_path = file_path
      system("mkdir -p #{FINAL_DIR}")
    end

    def fill_data
      prawn_file = "#{DOWNLOAD}/temp_#{Time.current.to_i}.pdf"
      output_file = "#{FINAL_DIR}/#{file_path.split('/').last}"
      hash = data_hash
      Prawn::Document.generate(prawn_file) do |file|
        # coordinates are generated with hit and trial method
        file.text_box hash[:city], :at => [115, 335]
        file.text_box hash[:name], :at => [200, 290]
        file.start_new_page
      end
      if ::PDF::Toolkit.pdftk(prawn_file, "multibackground", file_path, "output", output_file)
        output_file
      else
        raise "PDF merging exception raised"
      end
    end

    def data_hash
      {
        city: "city name",
        name: "any string"
      }
    end
  end
  
  NOTE: system must have pdftk installed.