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LaTeX PDF Invoice Generator API

Generate professional PDF invoices with the LaTeX API, using precise tables, branded templates, and reliable compilation in your app.

Mar 3, 2026·8 min read·

tutorialapi

PDF invoices are one of the most common document generation tasks in SaaS products, internal tools, and client portals. Teams often start with HTML-to-PDF libraries, then run into the same problems: tables drift across pages, fonts render differently from machine to machine, and totals no longer line up cleanly on the printed page.

LaTeX solves those problems by design. It treats the page like a typesetting surface instead of a browser viewport, which makes it a strong fit for invoices that need stable spacing, professional typography, and predictable page breaks. For a deeper look at why LaTeX consistently outperforms browser-based rendering, see LaTeX vs. HTML-to-PDF.

Why LaTeX Wins for Invoices#

The main difference is reliability. HTML and CSS were designed for flexible screen layouts, while invoices need fixed, repeatable output. LaTeX gives you that repeatability without fighting the layout engine.

A Practical Invoice Generation Pattern#

The cleanest invoice generator follows a simple flow:

1. Store invoice data in a structured model.
2. Render that data into a LaTeX template.
3. Escape every user-supplied string before it reaches the template.
4. Send the generated source to the FormaTeX API.
5. Return the compiled PDF to the user or save it for later download.

For invoice apps, the data model usually includes:

• invoice metadata such as number, issue date, due date, and currency
• sender and recipient address blocks
• line items with quantity, rate, and amount
• tax or VAT rules
• optional notes, payment instructions, and branding assets

That structure matters because the PDF should be generated from canonical data, not from a visual editor that can drift over time. Reusable LaTeX templates with variable substitution make this pattern even more scalable across multiple invoice layouts.

interface InvoiceData {
  invoiceNumber: string;
  date: string;
  dueDate: string;
  currency: string;
  from: {
    name: string;
    address: string;
    email: string;
  };
  to: {
    name: string;
    address: string;
    email: string;
  };
  lineItems: {
    description: string;
    qty: number;
    rate: number;
  }[];
  taxRate: number;
}

function buildInvoiceLatex(data: InvoiceData): string {
  const subtotal = data.lineItems.reduce((sum, item) => sum + item.qty * item.rate, 0);
  const tax = subtotal * data.taxRate;
  const total = subtotal + tax;

  const formatCurrency = (amount: number) =>
    amount.toLocaleString("en-US", { minimumFractionDigits: 2, maximumFractionDigits: 2 });

  const lineItemRows = data.lineItems
    .map(
      (item) =>
        `${escapeLatex(item.description)} & ${item.qty} & \\${formatCurrency(item.rate)} & \\${formatCurrency(item.qty * item.rate)} \\\\`
    )
    .join("\n");

  return `
\\documentclass{article}
\\usepackage[margin=2cm]{geometry}
\\usepackage{booktabs}
\\usepackage{array}
\\usepackage{fontspec}
\\pagestyle{empty}

\\begin{document}

\\begin{flushright}
  {\\Large\\textbf{INVOICE}} \\\\[0.5em]
  \\textbf{Invoice \\#:} ${escapeLatex(data.invoiceNumber)} \\\\
  \\textbf{Date:} ${escapeLatex(data.date)} \\\\
  \\textbf{Due:} ${escapeLatex(data.dueDate)}
\\end{flushright}

\\vspace{1em}

\\begin{minipage}[t]{0.45\\textwidth}
  \\textbf{From} \\\\
  ${escapeLatex(data.from.name)} \\\\
  ${escapeLatex(data.from.address)} \\\\
  ${escapeLatex(data.from.email)}
\\end{minipage}
\\hfill
\\begin{minipage}[t]{0.45\\textwidth}
  \\textbf{Bill To} \\\\
  ${escapeLatex(data.to.name)} \\\\
  ${escapeLatex(data.to.address)} \\\\
  ${escapeLatex(data.to.email)}
\\end{minipage}

\\vspace{2em}

\\begin{tabular}{p{8cm} r r r}
\\toprule
Description & Qty & Rate & Amount \\\\
\\midrule
${lineItemRows}
\\midrule
  & \\multicolumn{2}{r}{Subtotal} & \\${formatCurrency(subtotal)} \\\\
  & \\multicolumn{2}{r}{Tax (${Math.round(data.taxRate * 100)}\\%)} & \\${formatCurrency(tax)} \\\\
\\midrule
  & \\multicolumn{2}{r}{\\textbf{Total}} & \\textbf{\\${formatCurrency(total)}} \\\\
\\bottomrule
\\end{tabular}

\\end{document}
`;
}

function escapeLatex(text: string): string {
  return text
    .replace(/\\/g, "\\textbackslash{}")
    .replace(/&/g, "\\&")
    .replace(/%/g, "\\%")
    .replace(/\$/g, "\\$")
    .replace(/#/g, "\\#")
    .replace(/_/g, "\\_")
    .replace(/\{/g, "\\{")
    .replace(/\}/g, "\\}")
    .replace(/~/g, "\\textasciitilde{}")
    .replace(/\^/g, "\\textasciicircum{}");
}

API Integration Options#

The FormaTeX API works well for invoices because the payload is small, the layout is deterministic, and the compiled PDF can be returned immediately to the end user.

LATEX=$(cat invoice-template.tex)

curl -X POST https://api.formatex.io/api/v1/compile \
  -H "X-API-Key: $FORMATEX_KEY" \
  -H "Content-Type: application/json" \
  -d "{\"content\": $(echo \"$LATEX\" | jq -Rs .), \"engine\": \"pdflatex\"}" \
  --output invoice-2026-0042.pdf

import io
import os
import requests
from flask import Flask, request, send_file

app = Flask(__name__)

def generate_invoice(invoice_data: dict) -> bytes:
    latex = build_invoice_latex(invoice_data)

    response = requests.post(
        "https://api.formatex.io/api/v1/compile",
        headers={"X-API-Key": os.environ["FORMATEX_KEY"]},
        json={"content": latex, "engine": "pdflatex"},
    )

    if not response.ok:
        error = response.json()
        raise RuntimeError(f"LaTeX error: {error.get('log', error.get('error'))}")

    return response.content

@app.route("/invoices/<int:invoice_id>/pdf")
def download_invoice(invoice_id):
    invoice = Invoice.query.get_or_404(invoice_id)
    pdf_bytes = generate_invoice(invoice.to_dict())
    return send_file(
        io.BytesIO(pdf_bytes),
        mimetype="application/pdf",
        download_name=f"invoice-{invoice_id}.pdf",
    )

async function generateInvoicePDF(data: InvoiceData): Promise<Buffer> {
  const latex = buildInvoiceLatex(data);

  const response = await fetch("https://api.formatex.io/api/v1/compile", {
    method: "POST",
    headers: {
      "X-API-Key": process.env.FORMATEX_KEY!,
      "Content-Type": "application/json",
    },
    body: JSON.stringify({ content: latex, engine: "pdflatex" }),
  });

  if (!response.ok) {
    const error = await response.json();
    throw new Error(error.log ?? error.error);
  }

  return Buffer.from(await response.arrayBuffer());
}

Common Failure Modes#

Even a good invoice template can fail if the implementation ignores edge cases. Watch for these issues early:

• long item descriptions that overflow the table column
• unescaped customer names, job titles, or notes that contain special LaTeX characters
• logos or signatures that are too large for the header area
• tax and subtotal rows that do not format correctly for international currencies
• page breaks that split totals away from the last line items

The safest approach is to test with realistic data, not just a clean demo invoice. Include a long description, a discount line, a zero-tax invoice, and at least one invoice with a logo so you can confirm the template behaves under pressure. The complete guide to LaTeX API error codes covers the compilation failures you are most likely to encounter during this testing phase.

When to Use pdfLaTeX vs XeLaTeX#

For most invoice products, pdflatex is the default choice because it is fast, widely compatible, and more than enough for standard business documents. It also keeps the operational surface area small: the fonts are predictable, the compilation path is simple, and the output is stable across environments.

Use xelatex when the invoice needs brand typography or Unicode-heavy content that depends on system fonts. That is common in international SaaS products, agencies with custom identity systems, or customer-facing invoice portals where the logo and headings need to match the rest of the brand package. For a detailed breakdown of the trade-offs, see XeLaTeX vs pdfLaTeX.

The practical rule is simple. If the invoice is mainly text, numbers, and a logo, pdflatex is usually enough. If the invoice needs a specific font stack or broader character coverage, move to xelatex and make that choice part of the plan tier or template settings.

Invoice Data Model Checklist#

The quality of the PDF depends on the quality of the data model behind it. A reliable generator should normalize the following fields before compilation:

• country-specific address formatting
• currency and decimal precision rules
• tax labels such as VAT, GST, or sales tax
• date formatting by locale
• optional notes, payment instructions, and purchase order references
• line-item metadata for discounts, credits, or recurring charges

This also makes downstream features easier to build. Once the invoice exists as structured data, you can reuse it for email delivery, customer portals, accounting exports, and internal audits without inventing a second representation of the same document.

Production Checklist#

Before shipping an invoice generator, make sure these pieces are in place:

1. Validate invoice data before rendering the template.
2. Escape every string that came from a user or database.
3. Keep totals, tax, and currency formatting server-side and deterministic.
4. Store the compiled PDF only when you need auditability or re-downloads.
5. Return clear error messages when LaTeX compilation fails.
6. Add test invoices that cover long text, logos, and multi-line addresses.

That checklist turns a demo into a production feature. It also makes support easier because the same input will always generate the same PDF.

If you want the feature to feel dependable from day one, add a small suite of sample invoices that exercise all the awkward cases: extremely long project names, a zero-value invoice, a partial payment, and a multi-page bill with enough rows to prove the table breaks cleanly. If your app generates high invoice volumes, bulk LaTeX PDF generation with concurrency and retry logic covers the patterns needed to handle that load reliably.

Get Started#

• Sign up for free — start building your invoice generator today
• API reference — full compilation endpoint documentation
• Dashboard — manage API keys and monitor usage

Related Articles#

• LaTeX API Document Templates That Scale — Reusable LaTeX templates for invoices, reports, and certificates with variable substitution patterns
• XeLaTeX vs pdfLaTeX — Unicode support, custom fonts, and speed comparison to help you pick the right engine for branded invoices
• LaTeX vs. HTML-to-PDF — Compares Puppeteer, wkhtmltopdf, and WeasyPrint against LaTeX for document generation use cases
• LaTeX API Error Codes: Complete Guide — Every compilation error code explained, including 422 failures from malformed invoice templates
• Bulk LaTeX PDF Generation via API — Batch thousands of personalized invoices with concurrency control and retry logic

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