code: func (f *Fpdf) Output(w io.Writer) error {
  	if f.err != nil {
  		return f.err
  	}
  	// dbg("Output")
  	if f.state < 3 {
  		f.Close()
  	}
  	_, err := f.buffer.WriteTo(w)
  	if err != nil {
  		f.err = err
  	}
  	return f.err
  }
docs: // Output sends the PDF document to the writer specified by w. No output will
  // take place if an error has occurred in the document generation process. w
  // remains open after this function returns. After returning, f is in a closed
  // state and its methods should not be called.