Reorder pages of a PDF to allow printing as a brochure

pdf_brochure.py

import sys, subprocess, tempfile, os.path, warnings

A4 = (595, 842)

source = sys.argv[1]
target = sys.argv[2]

pages = None
page_size = None

for l in subprocess.run(
    ["pdfinfo", source], stdout=subprocess.PIPE, text=True
).stdout.splitlines():
    k, *v = map(str.strip, l.split(":"))
    if k == "Pages":
        pages = int(v[0])
    elif k == "Page size":
        s = v[0].split(" ")
        if s[3] != "pts":
            warnings.warn(
                "Page size detected, but uses unknown units, falling back to A4"
            )
        page_size = A4
        page_size = (float(s[0]), float(s[2]))

if pages is None:
    raise RuntimeError("Couldn't detect number of pages")

if page_size is None:
    warnings.warn("Page size detected, but uses unknown units, falling back to A4")
    page_size = A4

tmpdir = tempfile.mkdtemp()

page_size_bytestring = " ".join(map(str, page_size)).encode()
with open(os.path.join(tmpdir, "empty.pdf"), "wb") as fh:
    fh.write(
        b"%PDF-1.7\n%\xc2\xa6\xc2\xa6\n1 0 obj\n<<\n/Type /Pages\n/Count 1\n/Kids [ 2 0 R ]\n>>\nendobj\n2 0 obj\n<<\n/Type /Page\n/Parent 1 0 R\n/MediaBox [ 0 0 "
        + page_size_bytestring
        + b" ]\n>>\nendobj\n3 0 obj\n<<\n/Type /Catalog\n/Pages 1 0 R\n>>\nendobj\nxref\n0 4\n0000000000 65535 f \n0000000015 00000 n \n0000000074 00000 n \n0000000147 00000 n \ntrailer\n<<\n/Size 4\n/Root 3 0 R\n/Info 1 0 R\n/ID <656d7074795f70616765>\n>>\nstartxref\n196\n%%EOF"
    )


pages_multipleof_four = (pages - 1) if (m := pages % 4) == 0 else pages + 3 - m
page_format = (
    f"%0{len(str(pages_multipleof_four))}d" if pages_multipleof_four > 9 else "%d"
)

split_proc = subprocess.run(["pdfseparate", source, os.path.join(tmpdir, page_format)])

if split_proc.returncode != 0:
    raise RuntimeError("PDF separation failed")


def f(y):
    x = 0
    while x < y:
        yield y
        yield x
        yield x + 1
        yield y - 1
        x += 2
        y -= 2


page_order = [
    page_format % (x + 1,) if x < pages else "empty.pdf"
    for x in f(pages_multipleof_four)
]


subprocess.run(
    [
        "pdfunite",
        *map(lambda x: os.path.join(tmpdir, x), page_order),
        target,
    ]
)

usage.md

python3 pdf_brochure.py source.pdf brochure.pdf

Tested with Python 3.8, will likely work with other Python 3.* versions.

Depends on https://repology.org/project/poppler (uses commands pdfinfo, pdfseparate and pdfunite)

Print the resulting file with these settings:

Setting	Value	Comment
Two-sided	Short Edge (Flip)	the less common two-sided print option
Pages per side	2	that's the brochure trick, ya know?
Page ordering	Left to right
Page Scaling	Fit to Printable Area	autoscaling magic
Auto Rotate and Center	off	if some pages are landscape oriented, it will behave weirdly without this
Orientation	portrait	stack the pages horizontally, not vertically