How to Validate a ZUGFeRD PDF with cURL

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This tutorial shows how to validate an existing ZUGFeRD or Factur-X hybrid invoice with cURL. 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 cURL?

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 cURL 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 shell sample uses cURL directly. Set the service URL, API key, and local input paths near the top of the script before running it.

How to Validate a ZUGFeRD PDF with cURL Code Example

#!/bin/sh

# 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.
API_URL="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
# API_URL="https://eu-api.pdfrest.com"

# Replace the API key and PDF path below with your own values.
API_KEY="xxxxxxxx-xxxx-xxxx-xxxx-xxxxxxxxxxxx" # Replace with your API key
ZUGFERD_PDF="/path/to/zugferd-invoice.pdf"

curl --location "$API_URL/validated-zugferd" \
  --header "Accept: application/json" \
  --header "Api-Key: $API_KEY" \
  --form "file=@$ZUGFERD_PDF;type=application/pdf"

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. curl --form builds the multipart body. The @ prefix uploads a local file, and cURL supplies the multipart boundary automatically.
Configure the request safely. Set API_URL, API_KEY, and the local input paths near the beginning of the script. The commented EU URL is an optional regional service setting.
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 command prints the service response. In an application script, inspect the HTTP result and JSON before treating a returned resource ID or validation result as usable. A receiving or accounts-payable service can continue an accepted path or send an unsuccessful result for review.

Beyond the Tutorial

In this cURL 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 cURL. 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.