Professional Guide to Creating Accessible and DRM-Protected ePubs

Here is the Professional Guide to Creating Accessible and DRM-Protected ePub Files, prepared by the ApplicaDigital team.

This document was born as a response to an urgent need in the digital publishing sector: preparing technically solid, accessible content that complies with international standards and is protected against unauthorized use.

With the entry into force of European Directive 2019/882, creating ePub files with semantic structure, clear navigation, and real accessibility ceases to be an option and becomes a shared responsibility. This guide focuses precisely on that critical phase: the technical preparation of content before applying any DRM layer.

At ApplicaDigital, we understand this ecosystem because we have spent years working with Adobe Content Server and helping publishers, libraries, and distributors ensure the quality, control, and sustainability of their digital publications.

We hope this guide will be useful as a reference resource, operational support, and starting point for more effective collaboration.

Regardless of the ePub version you choose, certain principles are fundamental for quality and DRM preparation.

1. Rigorous Validation: The Gold Standard

• Critical Importance: Before even thinking about DRM, your ePub file must be valid. Validation ensures that the file complies with ePub standard specifications. An invalid file may not render correctly on some devices, or worse, may be rejected or corrupted by DRM systems.
• EPUBCheck: It is the official and industry-standard tool for validating ePub files. Download it from the W3C site or use it through online services or integrated into editing software. An EPUBCheck report with no errors is the first and most important indicator of a DRM-ready ePub.

2. Impeccable Semantic Structure (HTML5 for ePub3)

An ePub is, in essence, a packaged website. The quality of your HTML (or XHTML in ePub2) is crucial.

• Correct Use of HTML Tags: Use HTML tags for their semantic purpose. For example, <h1> for the main title, <p> for paragraphs, <blockquote> for quotes, etc.
• For ePub3 (HTML5): Take advantage of HTML5 semantic tags like <section>, <article>, <aside>, <nav>, <figure>, <figcaption>. This not only improves structure and accessibility but also facilitates processing by reading systems and DRM.
• Navigation Document (nav document in ePub3): It is an XHTML file that contains the main table of contents of the book, using HTML lists (<ol><li><a href="...">...</a></li></ol>). It must include "landmarks" (reference points) using the epub:type attribute to identify key sections such as the cover, start of content (bodymatter), table of contents (toc), index, etc.
• NCX (ePub2 and Compatibility in ePub3): The toc.ncx file is mandatory in ePub2 and recommended as a fallback in ePub3 for compatibility with older devices. It defines the hierarchical table of contents.

3. Clean and Optimized Content

Text

• Styles with CSS: Define all aspects of presentation (fonts, margins, colors, etc.) through external CSS stylesheets. Avoid inline styles (style="...") in HTML tags as much as possible. This facilitates maintenance, ensures consistency, and is less likely to interfere with DRM processes.
• Encoding: Use UTF-8 to ensure correct display of all characters.

Images

• Optimal Formats: JPEG (for photographs and images with complex color gradations), PNG (for logos, illustrations with flat colors, or transparencies), GIF (for simple animations, although in ePub3, consider video or CSS animations) and SVG (for vector graphics, ideal in ePub3).
• Weight/Resolution Optimization: Images should have adequate resolution for screens (generally 72-150 ppi is sufficient). Compress images without perceptible quality loss.
• Alternative Text (alt): All images (<img>) must include a descriptive alt attribute. This is crucial for accessibility (screen readers) and is a validation requirement. If an image is purely decorative, use alt="".

Fonts

• Embedding: Always embed the fonts used in your ePub to ensure visual consistency across all devices. Declare fonts in CSS using @font-face.
• Licenses: Fundamental! Ensure that the licenses of the fonts you use allow embedding in digital publications and their distribution.
• Formats: WOFF2 is preferred for ePub3 due to its excellent compression, followed by WOFF, OpenType (OTF) and TrueType (TTF).

4. Precise and Complete Metadata (content.opf)

The content.opf file is the heart of the ePub, describing its content, structure, and metadata.

• Essential Dublin Core Elements: Ensure that the following metadata (minimum) are present and correct: <dc:title>, <dc:creator>, <dc:identifier> (ISBN), <dc:language>, <dc:publisher>, <dc:date>, <meta property="dcterms:modified">.
• Significance: Correct metadata is vital for cataloging, discoverability in stores and libraries, and for DRM systems to correctly identify and process the book.

5. Functional Table of Contents (TOC)

• A clear, accurate, and navigable TOC is essential for user experience.
• In ePub2, it is defined exclusively in the toc.ncx file.
• In ePub3, it is defined primarily in the nav document (XHTML). It is recommended to also include a toc.ncx for backward compatibility.
• Ensure that all links in the TOC work correctly and lead to the corresponding sections of the book.

6. Cover

• The cover image must be high quality.
• It must be correctly declared in the content.opf manifest with the cover-image property.
• In ePub2, additionally, it is referenced in the <guide> section of content.opf.
• In ePub3, the nav document can have a landmark epub:type="cover" pointing to the cover XHTML.

Once your ePub is technically solid and validated, it is almost ready for DRM.

Golden Principle

Practices to Avoid That Can Complicate DRM

• Non-Packageable External Resources: All fonts, images, CSS, JS, audio, and video must be inside the ePub file. Links to external CDNs or websites for these resources will not work once DRM is applied.
• Excessively Complex or Invasive Scripts: Scripts that drastically alter the document structure on load, or that attempt to make non-standard network calls, may be blocked or cause instability in DRM environments.
• Fonts with Problematic Licenses or Not Embedded: Font licenses must allow embedding and possible modification/obfuscation that some DRM systems perform.
• Non-Standard File Structure: File names with strange characters, incorrect paths, or a confusing directory structure can hinder processing.
• Malformed or Invalid HTML/XHTML: Even if some readers "tolerate" minor errors, DRM systems are generally stricter.

Key Best Practices for DRM Preparation

• Embedding and Correct Font Declaration: Check that all fonts are embedded and correctly referenced in CSS and in the content.opf manifest.
• Structural Integrity of ePub Package: Ensure that the container.xml file correctly points to the content.opf file, and that all listed files exist in the specified paths.
• Thorough Testing on Various Readers BEFORE the DRM Stage: Test your ePub (without DRM) on multiple devices and reading applications.

Crucial Clarification: Your Role and ApplicaDigital's

This document focuses on OPTIMAL preparation of the ePub file on your part. Creating a high-quality, validated, and standards-compliant ePub file is your responsibility and the best guarantee for a smooth process.

DRM application is a subsequent process that ApplicaDigital (or the system you use through us) will manage on the ePub file you provide, once it has been perfected by you. We handle the protection technology; you handle the excellence of the source content.

Before sending your ePub for DRM application with ApplicaDigital, verify these points: