Wrapper for pdftk which stamps particular pages with patch PDFs; see --help

signpdf.py

#!/usr/bin/env python3

import argparse
import os
import shutil
import string
import subprocess
import tempfile

# Ensure required executables exist
for prog in ('pdftk', 'ps2pdf'):
	if shutil.which(prog) is None:
		raise RuntimeError("The program {prog} is required".format(prog=prog))

def toBase26(num):
	digits = string.ascii_uppercase
	if num == 0:
		return digits[0]
	out = []
	while num:
		out.append(digits[int(num % 26)])
		num = int(num // 26)
	out.reverse()
	return ''.join(out)

parser = argparse.ArgumentParser(description="Patch particular pages of a PDF",
		epilog="Example: %(prog)s contract.pdf 2=sig-p2.pdf 3=sig-p3.pdf signed.pdf")

def pagePdfPair(string):
	try:
		(page, pdf) = string.split('=', 1)
		if not len(pdf):
			raise ValueError
	except ValueError:
		parser.error("Expected a page=PDF pair")
	try:
		page = int(page)
	except ValueError:
		parser.error("Page number must be an integer")
	if page < 1:
		parser.error("Page number must be greater than zero")
	return (page, pdf)

parser.add_argument('inputPdf', type=str,
		help="the input file, particular pages of which will be stamped")
parser.add_argument('patchPdfs', metavar="N=patchPdf", type=pagePdfPair, nargs='+',
		help="a page number and patch PDF pair")
parser.add_argument('outputPdf', type=str,
		help="the output file")
parser.add_argument('-f', '--force', action='store_true',
		help="force writing to the given output file even if it already exists")

args = parser.parse_args()

# Prevent overwriting output file
if not args.force and os.path.isfile(args.outputPdf):
	parser.error("Output file {filename} already exists and --force not specified".format(filename=args.outputPdf))

# Ensure all input files exist
if not os.path.isfile(args.inputPdf):
	parser.error("Input file {filename} doesn't exist".format(filename=args.inputPdf))
for (page, pdf) in args.patchPdfs:
	if not os.path.isfile(pdf):
		parser.error("Patch file {filename} doesn't exist".format(filename=pdf))

# Get number of pages in input file
data = subprocess.run(['pdftk', args.inputPdf, 'dump_data'], stdout=subprocess.PIPE, encoding='utf8')
totalPages = None
for line in data.stdout.splitlines():
	if line.startswith('NumberOfPages: '):
		totalPages = int(''.join(filter(str.isdigit, line)))
		break

# Check no patch page numbers are out of range
for (page, pdf) in args.patchPdfs:
	if page > totalPages:
		parser.error("The input PDF has a page count of {total}, so page {page} cannot be patched".format(total=totalPages, page=page))

# Sort patch pages by page number
# Python sorts by first member by default, which makes this easy
args.patchPdfs.sort()

def getPatchForPage(p):
	for (page, pdf) in args.patchPdfs:
		if page == p:
			return 'PATCH{handle}'.format(handle=toBase26(page))
	return 'BLANK'

# Get a temporary context directory
with tempfile.TemporaryDirectory() as tempdir:
	# Make a blank page PDF
	blankPdf = os.path.join(tempdir, 'blank.pdf')
	subprocess.run(['ps2pdf', '-sPAPERSIZE=a4', '-', blankPdf], input="")

	# Make a patch PDF with the same total number of pages as the input PDF
	pdftkargs = ['pdftk', 'BLANK={filename}'.format(filename=blankPdf)]
	for (page, pdf) in args.patchPdfs:
		pdftkargs.append('PATCH{handle}={filename}'.format(handle=toBase26(page), filename=pdf))
	pdftkargs.append('cat')
	for page in range(1, totalPages + 1):
		pdftkargs.append(getPatchForPage(page))
	pdftkargs.append('output')
	patchPdf = os.path.join(tempdir, 'patch.pdf')
	pdftkargs.append(patchPdf)
	subprocess.run(pdftkargs)

	# Stamp the patch PDF on the input PDF
	subprocess.run(['pdftk', args.inputPdf, 'multistamp', patchPdf, 'output', args.outputPdf])