code: def append_memory_pdf_to_writer(input_pdf: bytes,
                                  writer: PdfFileWriter,
                                  start_recto: bool = True) -> None:
      
      if not input_pdf:
          return
      if start_recto and writer.getNumPages() % 2 != 0:
          writer.addBlankPage()
          # ... suitable for double-sided printing
      infile = io.BytesIO(input_pdf)
      reader = PdfFileReader(infile)
      for page_num in range(reader.numPages):
          writer.addPage(reader.getPage(page_num))
docs: Appends a PDF (as bytes in memory) to a PyPDF2 writer.
  
      Args:
          input_pdf: the PDF, as ``bytes``
          writer: the writer
          start_recto: start a new right-hand page?