def append_memory_pdf_to_writer(input_pdf: bytes,
                                writer: PdfFileWriter,
                                start_recto: bool = True) -> None:
    """
    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?
    """
    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))