code: def add_to_writer(self,
                        writer: PdfFileWriter,
                        start_recto: bool = True) -> None:
          
          if self.is_html:
              pdf = get_pdf_from_html(
                  html=self.html,
                  header_html=self.header_html,
                  footer_html=self.footer_html,
                  wkhtmltopdf_filename=self.wkhtmltopdf_filename,
                  wkhtmltopdf_options=self.wkhtmltopdf_options)
              append_memory_pdf_to_writer(pdf, writer, start_recto=start_recto)
          elif self.is_filename:
              if start_recto and writer.getNumPages() % 2 != 0:
                  writer.addBlankPage()
              writer.appendPagesFromReader(PdfFileReader(
                  open(self.filename, 'rb')))
          else:
              raise AssertionError("PdfPlan: shouldn't get here!")
docs: Add the PDF described by this class to a PDF writer.
  
          Args:
              writer: a :class:`PyPDF2.PdfFileWriter`
              start_recto: start a new right-hand page?