How to Validate a ZUGFeRD PDF with PHP

This tutorial shows how to validate an existing ZUGFeRD or Factur-X hybrid invoice with PHP. It uses the pdfRest Create ZUGFeRD PDF API Tool to submit the invoice PDF to its validation endpoint and print the response without modifying the document.

Why Validate a ZUGFeRD PDF with PHP?

Receiving an invoice PDF is not the same as knowing that it is a usable hybrid electronic invoice. A validation step checks the ZUGFeRD or Factur-X package and its PDF/A conformance before a receiving, records, or accounts-payable workflow treats the file as an accepted result.

For example, a PHP intake service can validate supplier invoices as they arrive, retain the response with the processing record, and route an unsuccessful result for follow-up before the invoice enters an automated approval path. This gives operational teams a clear decision point rather than discovering a problem later in the workflow.

Validation does not repair or replace the submitted PDF. It reports on the existing hybrid invoice, allowing the calling application to preserve the original, request a corrected version, or route the document to a separate creation or remediation process when appropriate.

What the Request Does

The multipart request contains one PDF in the file field. The endpoint analyzes that existing document and returns validation information; it does not generate a replacement invoice or modify the supplied PDF.

The PHP samples use Guzzle and PSR-7 stream utilities. Install Guzzle with Composer when moving the code outside the repository and supply the API key through protected configuration.

How to Validate a ZUGFeRD PDF with PHP Code Example

require 'vendor/autoload.php';

use GuzzleHttp\Client;
use GuzzleHttp\Psr7\Request;
use GuzzleHttp\Psr7\Utils;

// Validate a hybrid ZUGFeRD / Factur-X PDF without modifying it.
// By default, we use the US-based API service. This is the primary endpoint for global use.
$apiUrl = 'https://api.pdfrest.com';

/* For GDPR compliance and enhanced performance for European users, you can switch to the EU-based service by uncommenting the URL below.
 * For more information visit https://pdfrest.com/pricing#how-do-eu-gdpr-api-calls-work
 */
//$apiUrl = 'https://eu-api.pdfrest.com';

// Set this path to the completed hybrid ZUGFeRD or Factur-X PDF you want to validate.
$apiKey = 'xxxxxxxx-xxxx-xxxx-xxxx-xxxxxxxxxxxx';
$zugferdPdf = '/path/to/zugferd-invoice.pdf';

$client = new Client();
$headers = ['Accept' => 'application/json', 'Api-Key' => $apiKey];
$options = [
    'multipart' => [['name' => 'file', 'contents' => Utils::tryFopen($zugferdPdf, 'r'), 'filename' => basename($zugferdPdf), 'headers' => ['Content-Type' => 'application/pdf']]],
];
$request = new Request('POST', $apiUrl . '/validated-zugferd', $headers);
$response = $client->sendAsync($request, $options)->wait();
echo $response->getBody();

Source: View the multipart sample on GitHub.

Breaking Down the Code

The request is compact, but each field has a distinct role in the hybrid-invoice workflow.

• Submit the finished hybrid invoice. Validation accepts one existing ZUGFeRD or Factur-X PDF through the file field. The code sends it as application/pdf and does not include XML, pdf_file, regenerate_pdf, or render_options.
• Build the multipart request. Guzzle receives the multipart body as an array. File entries provide an opened stream, filename, and content type; text entries carry the ordinary API options.
• Configure the request safely. Configure the endpoint, key, and input paths before running the sample. Use Composer-managed Guzzle dependencies and keep the credential in protected application configuration.
• Call the validation endpoint. The request goes to /validated-zugferd, which is the validation endpoint within the Create ZUGFeRD PDF API Tool. It analyzes the submitted document without replacing or modifying it.
• Use the result as a workflow decision. The response body is printed as JSON. Check the HTTP status before accepting the result so an error document is not confused with a successful output or validation response. A receiving or accounts-payable service can continue an accepted path or send an unsuccessful result for review.

Beyond the Tutorial

In this PHP tutorial, you submitted an existing hybrid invoice for validation and handled the returned result as application data. That pattern fits an intake gate, a supplier-invoice check, or a controlled audit record.

For the complete request fields, accepted values, response contract, and service limits, review the Create ZUGFeRD PDF API Tool documentation for the validation endpoint. The same endpoint can be used with multipart uploads when the files are present in the current request or with resource IDs after a separate upload step.

The repository also includes a JSON-payload Validate ZUGFeRD PDF sample for PHP. That version uploads the source files first and then sends their resource IDs to /validated-zugferd, which is useful when a service already stages input files for later operations.