rails pdf suddenly render encrypted text instead of function to download pdf

Question

I have an app that have the function to download pdf. It was working all fine, but after several commit my pdf function just render encrypted text. the function that trigger the pdf link

  def print_pdf
    airwaybill = Airwaybill.find(params[:airwaybill_id])
    pdf = InvoicePdf.new(airwaybill, current_user)
    puts "#{}"
    send_data pdf.render, filename: "Airwaybill(#{airwaybill.airwaybill_no}).pdf" , type: 'application.pdf'
  end

what could be the most common problem for this issue?