What is PDF/A?
This article explains what PDF/A is and how it differs from a standard PDF. It covers the requirements for PDF/A compliance and the available versions and conformance levels. You'll also learn how to verify PDF/A compliance.
PDF/A is a subset of PDF defined by the ISO 19005 family of standards and designed for the long-term preservation of documents. Unlike regular PDFs, PDF/A documents must be completely self-contained so that they can be rendered consistently many years in the future.
Why use PDF/A format?
The goal of PDF/A is not to replace standard PDF, but to provide a reliable format for archiving documents. Use PDF/A when you need to:
- Store documents for years.
- Produce documents that look the same on every device.
- Satisfy legal and regulatory standards.
The PDF format was originally designed to preserve the visual appearance of documents across different devices and operating systems. However, a standard PDF document is not guaranteed to render consistently many years in the future.
For example, a PDF may reference fonts that are not embedded in the file, causing text to appear differently if those fonts are unavailable. A PDF may also contain JavaScript, multimedia, encryption, or links to external content that could become unsupported or inaccessible over time.
To address these challenges, the International Organization for Standardization (ISO) introduced PDF/A as a specialized version of PDF for long-term document preservation. PDF/A requires that all information needed to display a document correctly be stored within the file itself. It also prohibits features that could compromise future accessibility or consistent rendering.
Who uses PDF/A?
Government agencies, national archives, courts, healthcare providers, financial institutions, and businesses commonly rely on PDF/A for contracts, invoices, technical documentation, or reports. Regardless of the industry, the primary goal is the same: keep important documents accessible, searchable, and visually consistent throughout the preservation period.
Several standards and specifications are based on PDF/A:
- Factur-X / ZUGFeRD for electronic invoices. It is used for automated accounting, B2B and B2G e-invoicing, and paperless tax compliance across Europe.
- Order-X for electronic purchase orders. It is the counterpart to Factur-X for the ordering phase.
- EA-PDF for the long-term preservation of email messages. It is used by national archives and libraries.
PDF vs PDF/A differences
PDF/A is a subset of the PDF specification. Every PDF/A file is a PDF, but not every PDF document complies with the PDF/A standard.
The following table summarizes the key differences between standard PDF and PDF/A.
| Feature | Standard PDF | PDF/A |
|---|---|---|
| Embedding of used fonts | Optional | Required |
| Device-dependent colors | Allowed | Not allowed |
| Encryption and password protection | Allowed | Not allowed |
| External content | Allowed | Not allowed |
| Transparency | Allowed | Allowed in PDF/A-2+ |
| Optional content (layers) | Allowed | Allowed in PDF/A-2+ |
| File attachments | Allowed | Allowed in PDF/A-2+ |
| JavaScript | Allowed | Limited support in PDF/A-4 |
| 3D engineering content | Allowed | Allowed in PDF/A-4e |
PDF/A format requirements
A document is only considered PDF/A if it satisfies all requirements of the chosen PDF/A conformance level. You can find the list of all requirements in the veraPDF wiki.
Some of the most important PDF/A requirements are:
- All used fonts must be embedded.
- Colors must use explicitly defined color profiles.
- Metadata must follow specific rules.
- Encryption is not allowed.
As of July 2026, the PDF/A standard has four versions. Each version is based on a newer version of the PDF specification and defines several conformance levels.
PDF/A-1
| ISO standard | ISO 19005-1:2005 |
| Based on | PDF 1.4 |
| Conformance levels | A (PDF/A-1a), B (PDF/A-1b) |
PDF/A-1 does not allow embedded files, optional content (layers), transparency, and JPEG2000 images.
Level B means "Basic" conformance. It guarantees that the visual appearance of the document is preserved over time.
Level A means "Accessible" conformance. It includes all Level B requirements and extra requirements for accessibility:
- All document fonts must have Unicode mappings.
- Document should be marked as conforming to tagged PDF conventions.
- Document should contain a valid structure tree.
PDF/A-2
| ISO standard | ISO 19005-2:2011 |
| Based on | PDF 1.7 |
| Conformance levels | A (PDF/A-2a), B (PDF/A-2b), U (PDF/A-2u) |
PDF/A-2 extends PDF/A-1 by allowing transparency, optional content (layers), and JPEG2000 images. It also allows embedding of files that comply with PDF/A-1 or PDF/A-2.
Levels A ("Accessible") and B ("Basic") are similar to those in PDF/A-1.
Level U means "Unicode" conformance. It includes all Level B requirements with the additional requirement that all text in the document is properly mapped to Unicode. This is the preferred output format for OCR-generated PDFs.
PDF/A-3
| ISO standard | ISO 19005-3:2012 |
| Based on | PDF 1.7 |
| Conformance levels | A (PDF/A-3a), B (PDF/A-3b), U (PDF/A-3u) |
PDF/A-3 is identical to PDF/A-2 except that it allows embedded files of any type.
Factur-X / ZUGFeRD and Order-X standards are based on PDF/A-3.
PDF/A-4
| ISO standard | ISO 19005-4:2020 |
| Based on | PDF 2.0 |
| Conformance levels | PDF/A-4, E (PDF/A-4e), F (PDF/A-4f) |
The most modern PDF/A version. Unlike older conformance levels, PDF/A-4 supports JavaScript actions. It also supports PDF Advanced Electronic Signatures (PAdES).
PDF/A-4f allows arbitrary PDF attachments, while PDF/A-4 requires attachments to comply with PDF/A-1, PDF/A-2, or PDF/A-4.
PDF/A-4e replaces the old PDF/E standard to support 3D models in engineering workflows.
How to choose a PDF/A version
The "right" PDF/A version depends on what you need from your archived documents. If you're unsure, choose PDF/A-4. It is the newest version of the standard, preserves more PDF features, and is suitable for most archiving scenarios. Use the following recommendations:
| Requirement | Recommended PDF/A level |
|---|---|
| Maximum compatibility with older software | PDF/A-1 |
| Maximum accessibility | PDF/A-2a or PDF/A-3a |
| Transparency, layers, JPEG2000 images | PDF/A-2+ |
| Searchable text | PDF/A-2u or PDF/A-3u |
| Factur-X / ZUGFeRD | PDF/A-3 |
| New projects | PDF/A-4 |
| Preserve arbitrary attachments | PDF/A-4f |
Convert PDF to PDF/A
Converting an existing PDF to PDF/A is often the easiest way to prepare documents for archival. During conversion, the document is analyzed and modified if necessary to comply with the selected PDF/A conformance level.
Depending on the source document, the conversion process may involve:
- Embedding missing fonts.
- Adding output intents.
- Replacing unsupported color spaces.
- Removing prohibited features such as JavaScript or encryption.
Some PDF features cannot be preserved in every PDF/A version. For example, converting to PDF/A-1 may require removing transparency, layers, or embedded files because these features are not permitted by the standard.
Read the Convert PDF to PDF/A article for more information.
Verify PDF/A compliance
Converting a document to PDF/A is only part of the process. The resulting document should also be validated for PDF/A compliance.
PDF/A documents include XMP metadata that identifies the claimed PDF/A version and conformance level. Is checking the metadata enough for PDF/A verification? No! Metadata does not prove that the document is PDF/A-compliant. A document may contain PDF/A identification metadata while still violating PDF/A requirements.
Reliable validation checks the entire document, including its structure, fonts, colors, annotations, metadata, embedded files, and other features defined by the PDF/A specification. Validation helps you:
- Confirm that the document conforms to the intended PDF/A conformance level.
- Detect issues that could compromise long-term preservation.
- Ensure compliance with organizational or regulatory requirements.
- Identify issues before archiving or distributing documents.
Among the available PDF/A validators, veraPDF and Adobe Acrobat Preflight are generally regarded as the most reliable.
veraPDF is an open-source validator specifically designed to validate PDF/A documents against the ISO standard. It is widely used by archives, libraries, and software vendors.
Adobe Acrobat Preflight is Adobe's proprietary document analysis and validation tool. Since Adobe created the PDF format, Preflight is considered an authoritative validator and is frequently used to verify PDF/A compliance in production workflows.
No validator is perfect, and minor differences in interpretation of the specification can occur. For example, veraPDF and Adobe Acrobat Preflight treat pdfaSchema:schema values differently.
When validation results disagree, check the relevant ISO specification to determine whether the reported issue represents a real compliance problem. If a document passes validation in both veraPDF and Adobe Acrobat Preflight, you can be confident that it is PDF/A-compliant.
Frequently Asked Questions
What are PDF/A advantages over other formats?
PDF/A combines the visual consistency of PDF with the long-term preservation guarantees required for archiving. Compared to other common document formats, it offers several important advantages:
- Microsoft Word (DOC/DOCX)
Word documents depend on the software, fonts, and system configuration used to open them. Their appearance can change between versions of Microsoft Word or other editors. - TIFF
With TIFF, document pages are stored as images, making files much larger than PDF/A files. Images do not allow text search, text selection, and accessibility unless OCR data is added separately. - HTML
Web pages depend on external resources such as fonts, stylesheets, images, and scripts. These dependencies may change or disappear over time. - Standard PDF
A regular PDF may contain external dependencies, encryption, JavaScript, multimedia, or other features that can become unavailable over time.
Is PDF/A editable?
PDF/A files can be edited like ordinary PDF documents, but the modified document must be re-validated for PDF/A compliance.
Are PDF/A files smaller than PDF?
PDF/A files are usually larger than corresponding PDF files. PDF/A files typically include embedded fonts, ICC profiles, and other resources required to render the document consistently.
Can I open PDF/A files in a regular PDF reader?
Yes. Every valid PDF/A file is also a valid PDF file.
Which PDF/A version should I use?
Read the How to choose a PDF/A version section.
How to automate PDF to PDF/A conversion?
Use the Docotic.Pdf library. The Convert PDF to PDF/A article explains how to automate different conversion scenarios.
How to validate PDF/A documents?
Use veraPDF or Adobe Acrobat Preflight to verify PDF/A compliance. veraPDF is an excellent choice for automated workflows, while Acrobat Preflight is widely used for interactive validation.
Try the PdfToPdfa application for batch PDF-to-PDF/A conversion and validation. This application uses Docotic.Pdf for conversion and veraPDF for validation.
How to generate PDF/A documents from HTML?
Check the HTML to PDF/A section.
Visit our
LinkedIn page |
Telegram channel |
Google Group