Combine two A5 PDF pages to one A4 PDF page.

combine_a5.py

from pathlib import Path

from pikepdf import *

a5_pdf_path = Path('A5_PDF_PATH')
a4_output_path = Path('A4_OUTPUT_PATH')

a4_pdf = Pdf.new()
a4_pdf.add_blank_page(page_size=(595, 842))
destination_page = a4_pdf.pages[0]

with Pdf.open(a5_pdf_path) as a5_pdf:
    a5_page = a5_pdf.pages[0]
    a5_trimbox = Rectangle(a5_page.trimbox)
    destination_page.add_overlay(a5_page, a5_trimbox)
    y_offset = 421
    a5_trimbox.lly += y_offset
    a5_trimbox.ury += y_offset
    destination_page.add_overlay(a5_page, a5_trimbox)

a4_pdf.save(a4_output_path)