Converts each cells in tbe notebook to a PDF named something like
    'q04c.pdf'. Places PDFs in the specified folder and returns the list of
    created PDF locations.

def create_question_pdfs(nb, pages_per_q, folder, zoom) -> list:
    """
    Converts each cells in tbe notebook to a PDF named something like
    'q04c.pdf'. Places PDFs in the specified folder and returns the list of
    created PDF locations.
    """
    html_cells = nb_to_html_cells(nb)
    q_nums = nb_to_q_nums(nb)

    os.makedirs(folder, exist_ok=True)

    pdf_options = PDF_OPTS.copy()
    pdf_options['zoom'] = ZOOM_FACTOR * zoom

    pdf_names = []
    for question, cell in zip(q_nums, html_cells):
        # Create question PDFs
        pdf_name = os.path.join(folder, '{}.pdf'.format(question))

        pdfkit.from_string(cell.prettify(), pdf_name, options=pdf_options)

        pad_pdf_pages(pdf_name, pages_per_q)

        print('Created ' + pdf_name)
        pdf_names.append(pdf_name)
    return pdf_names