for i in....     
            # Create one pdf file per tiff file
            with open(str(i) + '.pdf', "wb") as f, io.BytesIO() as output:
                img = PIL.Image.open(str(i) + '.tiff')
                img.save(output, format='tiff')
                f.write(img2pdf.convert(output.getvalue()))

# merge the pdf file into one output pdf file
pdf_writer = PdfFileWriter()

output_file = publication_number + ".pdf"
file_list = os.listdir()
pdf_list = []
for file in file_list:
    if file.endswith(".pdf"):
        pdf_list.append(file)
pdf_list.sort(key=lambda f: int(
    ''.join(filter(str.isdigit, f))))  # trier la liste d'image du plus petit au plus grand (et pas 1, 10, 11, 2, 3)

for pdf_file in pdf_list:
    pdf_reader = PdfFileReader(pdf_file)
    for page in range(pdf_reader.getNumPages()):
        pdf_writer.addPage(pdf_reader.getPage(page))
with open(output_file, 'wb') as fh:
    pdf_writer.write(fh)

for i in range(1, max_page + 1):  
    os.remove(str(i) + '.tiff')
    os.remove(str(i) + '.pdf')