Generate PDF with wkhtmltopdf without any required gems. In this case I use rails, but it's flexible for any ruby frameworks or just for simply ruby app

gistfile1.rb

def show
  @pet = Pet.find(params[:id])
  tempfile = Tempfile.new(@pet.id.to_s)
  render_file = Tempfile.new(@pet.id.to_s + '.html')
  buffer = render  'show.pdf.erb', layout: false
  render_file.write(buffer.first)

  html = "#{render_file.path}.html"
  system "mv #{render_file.path} #{html} && wkhtmltopdf #{html} #{tempfile.path}"
  send_file tempfile.path, type: 'application/pdf'
end