Contract PDFs in Django

Why contracts become PDFs

A contract has to be fixed at signature. Both parties need to be certain they are looking at identical words, which a rendered page cannot guarantee. That is the difference between a document and a view of a database, and it is why legal and sales operations keep asking for this.

What a contract has to carry

Before any of the code below matters, the template has to produce a document that is actually a contract. These are the fields that make it one, and the ones a reader or an auditor will look for first.

• the parties, by legal entity name and registered number
• the effective date and the term
• numbered clauses with stable numbering, since amendments reference them
• the commercial schedule, usually as an annexe rather than in the body
• signature blocks with name, title and date for each party

Turning your the Django template language template into a document

You already have the markup. Render_to_string("invoices/detail.html", context) gives you it as a string, which is the only input the render needs. Django resolves {% static %} to a path relative to STATIC_URL, which means the stylesheet URL in your rendered HTML is only meaningful to a browser that already has a session on your host. A renderer fetching it from outside gets a 404 and produces an unstyled document. Inline the CSS into the string you send, or make STATIC_URL absolute for this one code path.

The Django implementation

httpx is the client most projects here already have. The render happens in a view that returns FileResponse, and you hand the bytes back as a FileResponse with an explicit content type.

# views.py
import httpx
from django.conf import settings
from django.http import FileResponse
from django.shortcuts import get_object_or_404
from django.template.loader import render_to_string

from .models import Contract


def contract_pdf(request, pk):
    contract = get_object_or_404(Contract, pk=pk)

    # A template that extends nothing. The on-screen template carries base.html,
    # the nav and the messages block, none of which belong in a contract.
    html = render_to_string("contracts/pdf.html", {"contract": contract})

    upstream = httpx.stream(
        "POST",
        "https://api.pdfpipe.xyz/v1/pdf",
        headers={"Authorization": f"Bearer {settings.PDFPIPE_KEY}"},
        json={"html": html, "options": {"format": "A4", "printBackground": True}},
        timeout=60.0,
    )

    response = upstream.__enter__()
    response.raise_for_status()

    return FileResponse(
        response.iter_bytes(),
        content_type="application/pdf",
        filename=f"contract-{contract.reference}.pdf",
    )

The CSS that makes a contract page correctly

The layout problem specific to this document is that numbered clauses with cross-references, where a page break in the wrong place separates a clause from the term it defines. These rules handle it.

/* A clause must not be separated from the term it defines, and a
   signature block alone on a final page invites a dispute. */
.clause     { break-inside: avoid; }
.signatures { break-inside: avoid; break-before: avoid; }

p { orphans: 3; widows: 3; }

@page { size: A4; margin: 25mm 20mm; }

What goes wrong in Django

The template that renders your on-screen view is almost always the wrong one to send. It carries the base layout, the nav, and the messages framework, all of which land in the PDF. Render a template that extends nothing, and keep it beside the view template so the two do not drift.

What people try first

Most Django projects reach for WeasyPrint or xhtml2pdf, both of which put layout in your Python process. WeasyPrint needs Cairo and Pango in the image; xhtml2pdf supports a subset of CSS that stopped growing years ago. That works until it is running on more than one machine, at which point the browser becomes the thing you operate rather than the thing you use.

Where the contract lives afterwards

Rendering is the short part. A contract is retained for the term plus the limitation period, which typically means well over a decade. Immutability matters more here than anywhere else on this list: both parties must be able to prove the words have not moved.

Getting the document right

• Check the parties and the effective date, which is what every later dispute turns on.
• Generation is triggered by agreement being reached, often with a signature workflow following, so size the timeout for that path rather than for a health check.
• These are produced one at a time by a person who is waiting, so latency is felt directly.
• Backgrounds are painted by default here, so a design that uses colour needs nothing set. Only an explicit print_background of false turns them off.

Frequently asked

Related

Other Django documents, and the same contract in other stacks.