How to generate PDF invoices from JSON without layout libraries

The problem with traditional PDF libraries (mPDF, FPDF, iText, PDFSharp)

Old-style PDF rendering libraries (whether in PHP, Node.js, C#, or Python) present three fundamental problems for modern software houses:

• Coupling between data and layout: the code that fetches data from the database is mixed with the graphic instructions that draw the tables.
• Poor flexibility: changing an invoice template requires code changes and deploy cycles.
• Resource consumption: generating large PDFs is a CPU-intensive operation that can slow down the main application if it is not properly isolated.

Separating data from design is the solution: the backend application only needs to collect the data, format it into a clean JSON object, and send it to a document generation API that returns a ready PDF. If you are looking for how to generate PDFs from JSON, create PDF invoices via API, or an alternative to C# / PHP / Node PDF libraries, this is the modern JSON-to-PDF pattern.

Step 1: structure the invoice JSON payload

The first step is to define the data structure. A well-designed JSON dictionary for an invoice must contain issuer data, customer data, document metadata, and the array of line items.

Here is an example of a standardized payload (copy it and adapt it to your template schema):

{
  "documento": {
    "tipo": "Fattura Differita",
    "numero": "FPA-2026-1044",
    "data": "18/07/2026",
    "valuta": "EUR"
  },
  "emittente": {
    "ragione_sociale": "Sviluppo Software S.r.l.",
    "partita_iva": "IT01234567890",
    "indirizzo": "Via dell'Innovazione 42",
    "cap_citta": "66034 Lanciano (CH)",
    "email": "amministrazione@softwarehouse.it"
  },
  "cliente": {
    "ragione_sociale": "Azienda Cliente SpA",
    "partita_iva": "IT09876543210",
    "indirizzo": "Corso Vittorio Emanuele II, 100",
    "cap_citta": "00100 Roma (RM)"
  },
  "righe_fattura": [
    {
      "codice": "SW-SAAS-01",
      "descrizione": "Abbonamento Cloud SaaS QuartzAPI - Licenza Enterprise (Mensile)",
      "quantita": 1,
      "prezzo_unitario": 249.00,
      "aliquota_iva": 22
    },
    {
      "codice": "CONS-PRO-02",
      "descrizione": "Attività di integrazione sistemi ERP e configurazione Webhook",
      "quantita": 8,
      "prezzo_unitario": 75.00,
      "aliquota_iva": 22
    }
  ],
  "totali": {
    "imponibile": 849.00,
    "imposta": 186.78,
    "totale_documento": 1035.78
  }
}

Step 2: configure the template on the cloud portal

Instead of coding foreach loops to print table rows in the PDF, you upload a graphic template (visual Template Builder) to the QuartzAPI portal. In the template you insert placeholders that match the JSON keys (e.g. a field bound to cliente.ragione_sociale).

The engine reads the righe_fattura array and automatically iterates the table Details band, calculating where to break the page if items span 2, 3, or more pages, while keeping the header and footer. No X/Y coordinates to write in your business application.

Step 3: call the Web API to generate the PDF

Once the template is configured (template code in the portal, e.g. INVOICE1) and you have the API key, your application sends an HTTP POST request. QuartzAPI generates the PDF and can save it in a document folder (folderId) ready for download and email delivery.

Endpoint: POST …/index.php?r=api/v1-jobs/generate-document — body with templateCode, data (the JSON above) and optional folderId. Documentation: Web API.

Example in Node.js (Axios)

const axios = require('axios');

const payloadFattura = { /* ... the JSON defined above ... */ };

async function generaFattura() {
  try {
    const response = await axios.post(
      'https://backend.quartzapi.com/index.php?r=api/v1-jobs/generate-document',
      {
        templateCode: 'INVOICE1',
        folderId: 'fld_ESEMPIO_CARTELLA',
        externalId: 'FPA-2026-1044',
        outputFormat: 'pdf',
        data: payloadFattura
      },
      {
        headers: {
          Authorization: 'Bearer TUO_API_KEY_SEGRETA',
          'Content-Type': 'application/json'
        }
      }
    );

    console.log('PDF generated successfully!', response.data);
    // result.documentId and downloadUrl for secure download
  } catch (error) {
    console.error(
      'Error during PDF generation:',
      error.response ? error.response.data : error.message
    );
  }
}

generaFattura();

Example in PHP (cURL)

<?php

$payloadFattura = [ /* ... the JSON dictionary as a PHP array ... */ ];

$ch = curl_init('https://backend.quartzapi.com/index.php?r=api/v1-jobs/generate-document');
curl_setopt($ch, CURLOPT_RETURNTRANSFER, true);
curl_setopt($ch, CURLOPT_POST, true);
curl_setopt($ch, CURLOPT_POSTFIELDS, json_encode([
    'templateCode' => 'INVOICE1',
    'folderId' => 'fld_ESEMPIO_CARTELLA',
    'externalId' => 'FPA-2026-1044',
    'outputFormat' => 'pdf',
    'data' => $payloadFattura,
]));
curl_setopt($ch, CURLOPT_HTTPHEADER, [
    'Authorization: Bearer TUO_API_KEY_SEGRETA',
    'Content-Type: application/json',
]);

$response = curl_exec($ch);
if (curl_errno($ch)) {
    echo 'cURL error: ' . curl_error($ch);
} else {
    $data = json_decode($response, true);
    echo 'Document saved. documentId: ' . ($data['result']['documentId'] ?? '');
}
curl_close($ch);

Next steps: download and automatic email delivery

One of the biggest advantages of an API-based approach is flexibility after generation. Since the PDF is stored in the portal folders:

• On-demand download: download the file with GET …/index.php?r=api/v1-documents/download&uid={documentId}.
• Built-in email delivery: call POST …/index.php?r=api/v1-jobs/send-document passing the documentId and the recipients. You can use the SMTP configured on the API key, without managing a complex mailer in your business app.

Conclusions

Treating PDF documents as graphic code to maintain is technical debt that software houses can no longer afford. Moving to a JSON-to-PDF architecture via API reduces development time, isolates the computational load, and allows non-technical roles to update templates without touching a single line of application code.

Ready to remove PDF libraries from your code? QuartzAPI is in public Beta: sign up for free, get your API key, and test invoice and report generation by sending your JSON objects.

👉 Start free with the QuartzAPI Beta