Choosing the right PDF standard can make a significant difference. Two of the most relevant ISO-certified standards for long-term, accessible digital documents are PDF/UA and PDF/A-3a. Although they sound similar, they serve very different purposes. Understanding the difference helps ensure compliance, accessibility, and reliability. TX Text Control allows you to generate both ISO standard types, but selecting the appropriate one for your specific needs can be challenging.

Preview

This article describes an upcoming feature of TX Text Control 34.0, planned for release in November 2025. PDF/UA and PDF/A-3a compliance will be fully supported in this version.

Understanding the Standards

What is PDF/A-3a?

PDF/A stands for "PDF for Archiving" and is an ISO standard (ISO 19005) designed for the long-term preservation of electronic documents. PDF/A-3, the third part of this standard, allows you to embed arbitrary files, such as XML, CSV, or DOCX, into a PDF. The "A" level adds full accessibility and structure, ensuring that the document:

• Embeds all fonts and metadata
• Contains no external dependencies
• Includes logical structure and tagging
• Ensures accessibility for assistive technologies (screen readers)

One common use case is a PDF invoice that embeds a machine-readable XML file (e.g., ZUGFeRD or Factur-X) to ensure e-invoicing compliance.

Learn More

This article shows how to create ZUGFeRD 2.3 compliant invoices using TX Text Control .NET Server. ZUGFeRD 2.3 is the latest version of the ZUGFeRD data model and complies with the European standard EN 16931. The article shows how to create ZUGFeRD 2.3 invoices and how to embed the XML invoice data in a PDF document.

Creating ZUGFeRD 2.3 (XRechnung, Factur-X) Documents with .NET C#

What is PDF/UA?

PDF/UA stands for "PDF/Universal Accessibility" (ISO 14289). The standard ensures that every user, including those who rely on assistive technologies, can read and navigate the document.

A PDF/UA document provides:

• Full semantic tagging (paragraphs, tables, lists)
• Alternative text for images and non-text elements
• Proper reading order and navigation
• Valid structure tree conforming to WCAG and Section 508 requirements
• Table summaries and headers for better comprehension

In short, PDF/UA ensures that your PDF is usable and understandable by all.

The Standards in Detail

Here is a detailed comparison of PDF/A-3a and PDF/UA:

Feature	PDF/A-3a	PDF/UA
Purpose	Long-term archiving with embedded files	Accessibility
File Embedding	Yes (e.g., XML, CSV)	No
Accessibility Features	Yes (tagging, structure)	Yes (full semantic tagging, alt text)
Compliance Standards	ISO 19005	ISO 14289
Use Cases	Invoices, legal documents	Public documents, educational materials
External Dependencies	No	No
Metadata Requirements	Mandatory	Recommended

Legal and Compliance Aspects

Both PDF/A-3a and PDF/UA carry legal implications. PDF/A-3a is often required for document retention in industries such as finance and healthcare. Meanwhile, PDF/UA compliance is essential for organizations to comply with accessibility laws, such as the Americans with Disabilities Act (ADA) and the European Accessibility Act.

Archival Compliance

PDF/A-3a is widely accepted for legal and financial archiving in both the EU and the US. It is often required by government regulations, tax authorities, and record-keeping laws. In Europe, standards such as ZUGFeRD and Factur-X use PDF/A-3 to combine human-readable invoices with machine-readable XML attachments.

Accessibility Compliance

Accessibility is becoming an increasingly important legal requirement. In the EU, the European Accessibility Act (EAA) and EN 301 549 require digital documents to be accessible by 2025. In the U.S., Section 508 of the Rehabilitation Act requires federal agencies to provide accessible digital content, including PDFs.

Organizations that publish digital information, such as reports, statements, contracts, and online forms, publicly must ensure PDF/UA compliance to avoid legal risks and discrimination claims.

Which Format Should You Use?

Your specific needs determine whether you should choose PDF/A-3a or PDF/UA.

Choose PDF/A-3a if:

• You need to archive documents for long-term retention.
• You want to embed additional files (e.g., XML invoices).
• Your industry requires compliance with archiving standards.

Choose PDF/UA if:

• You need to ensure accessibility for all users.
• Your documents are intended for public distribution.
• You want to comply with accessibility laws and regulations.

The Best of Both Worlds

The good news is that these standards are not mutually exclusive. A document can be compliant with both PDF/A-3a and PDF/UA at the same time. This combination is ideal for organizations that need archival stability and universal accessibility, such as governments, insurance companies, and financial institutions. If you use TX Text Control to generate your PDFs, you can easily create documents that meet both standards.

The following code generates a PDF/A-3a document that is automatically added and compliant with PDF/UA:

using System.Security.Cryptography.X509Certificates;
using TXTextControl;

// Define the certificate password and path
const string password = "123";
const string certificatePath = "certificate.pfx";

var cert = new X509Certificate2(certificatePath, password, X509KeyStorageFlags.Exportable);

// Initialize TXTextControl to create and save a document with the digital signature
using (var tx = new ServerTextControl())
{
    tx.Create();
    //tx.Load("test_file.tx", StreamType.InternalUnicodeFormat);
    tx.Text = "This document is digitally signed.";

    // Prepare the digital signature for the document
    var saveSettings = new SaveSettings
    {
        DigitalSignature = new DigitalSignature(cert, null)
    };

    // Save the document as a PDF with the digital signature
    tx.Save("result.pdf", StreamType.AdobePDFA, saveSettings);
}

The following screenshot shows the resulting PDF document opened in Adobe Acrobat Pro. As indicated by the respective conformance levels, the document is both PDF/A-3a and PDF/UA compliant.

Recommended Practices

The best choice between PDF/UA and PDF/A-3a depends on the nature of your documents and the requirements of your business processes. The most sustainable and future-proof strategy in modern environments is to combine both standards in a single workflow.

It is best to strive for dual compliance with both PDF/A-3a and PDF/UA in a single file. This ensures that each document can be legally archived and reproduced in the long term while remaining fully accessible to users who rely on assistive technologies. Fulfilling both standards meets legal, accessibility, and archival requirements in one step.

This combined approach is particularly relevant for organizations in regulated industries, such as government, finance, healthcare, and insurance. It prevents the costly and time-consuming process of regenerating archived documents when accessibility laws become mandatory in more jurisdictions. Rather than treating accessibility and long-term preservation as separate topics, they should be considered two dimensions of the same compliance goal.

Build Accessibility and Compliance into the Pipeline

With TX Text Control 34.0, generating valid PDF/UA and PDF/A-3a documents is easy. Simply provide the required metadata and alternative or descriptive texts for objects such as tables, links, and figures. TX Text Control will take care of the rest and generate valid PDF files. If you already have a process for generating PDFs based on templates, all you need to do is loop through the elements and provide descriptive text. TX Text Control provides a powerful API for this purpose.

You can also use LLMs to generate the necessary descriptive text, as described in the linked article below.

Learn More

This article shows how to use TX Text Control together with the OpenAI API to automatically add descriptive texts (alt text and labels) to images, links, and tables in a DOCX. The resulting document is then exported as a PDF/UA compliant PDF document.

Automating PDF/UA Accessibility with AI: Describing DOCX Documents Using TX Text Control and LLMs

Conclusion

For business applications that produce reports, contracts, or invoices, the combination of PDF/A-3a and PDF/UA offers the greatest value. These documents remain readable and verifiable decades later while being usable by everyone today. Accessibility and longevity are complementary qualities, not competing objectives. By choosing this hybrid standard, your organization can meet current and future regulatory requirements while maintaining the highest level of document quality and inclusivity.