Best practices for PDF accessibility and screen readers

Understanding the Root Cause Untagged PDFs

Many PDFs generated from scans, legacy software, or direct exports often lack proper internal structure, known as "tags." Without these foundational tags, screen readers cannot interpret the document's content, discern the logical reading order, or understand its hierarchical structure. This deficiency renders the PDF effectively invisible and inaccessible to users relying on assistive technologies.

Essential Best Practices for Accessible PDFs

Implement Proper Document Structure and Tags

Tags are the semantic backbone of PDF accessibility. They define elements like headings, paragraphs, lists, and tables, enabling screen readers to communicate the document's layout and content relationships accurately.

• Use Semantic Tags: Map your document's logical structure to appropriate PDF tags. Utilize H1 for main titles, H2-H6 for subheadings, P for paragraphs, L for lists, and LI for list items.
• Establish Logical Reading Order: Ensure the tag order within the PDF matches the visual reading flow. Screen readers follow this sequence strictly, and a jumbled order makes content incomprehensible.
• Tag Tables Correctly: Employ Table, TR (table row), TH (table header), and TD (table data) tags. Explicitly define row and column headers to provide essential context for data cells.
• Nest Lists Properly: For hierarchical lists, ensure sub-lists are correctly nested within parent list items using the appropriate LBody and L tags.

Provide Descriptive Alternative Text for Images

Images, charts, and graphs are visual elements that require textual equivalents for users of screen readers. This is the primary function of Alt Text.

• Convey Information Concisely: Alt text must describe the image's content and its purpose within the document. For complex charts, provide a summary or reference a more detailed description in the document body.
• Mark Decorative Images: Images that serve a purely aesthetic purpose should be marked as decorative (often by leaving alt text blank or setting it to an empty string in authoring tools), preventing screen readers from announcing them unnecessarily.

Utilize Bookmarks and Logical Navigation

Bookmarks function as a navigable table of contents, allowing users to quickly jump to relevant sections, which is particularly crucial for long documents.

• Create a Hierarchical Structure: Organize bookmarks to mirror the document's heading structure, with main sections as top-level bookmarks and sub-sections nested appropriately.
• Ensure Descriptive Titles: Bookmark titles should clearly and accurately indicate the destination content.

Specify Document Language

Defining the primary language of the PDF enables screen readers to use the correct pronunciation, intonation, and dictionary for accurate content delivery.

• Define Primary Language: In the document properties, specify the default language (e.g., English, Spanish, French).
• Identify Language Changes: For specific text blocks or sections written in a different language, apply a language tag to that particular content to ensure correct interpretation.

Make Form Fields Accessible

For interactive PDFs containing form fields, robust accessibility is paramount to ensure all users can complete and submit information.

• Add Labels and Tooltips: Every form field must have an associated, programmatically determined label that a screen reader can announce. Tooltips can provide additional instructions or context.
• Define Tab Order: Ensure the tab order follows a logical, sequential path through the form fields, allowing users to navigate efficiently.

Address Scanned Documents with OCR

Scanned PDFs are essentially images of text, rendering them completely inaccessible to screen readers because there is no selectable text to read. Optical Character Recognition (OCR) is indispensable for converting these image-based documents into machine-readable text.

• Apply OCR Thoroughly: Utilize a robust OCR tool to process scanned documents. This process converts the image into selectable, searchable text, making the content available to screen readers.
• Verify OCR Output: After performing OCR, always visually inspect the document for any recognition errors, especially in critical data or complex formatting, and make necessary corrections. For quick and reliable text extraction from scanned PDFs, consider using our OCR PDF tool.

Validating PDF Accessibility

Even with meticulous application of best practices, validation is a critical final step to ensure compliance with accessibility standards like WCAG (Web Content Accessibility Guidelines) and PDF/UA (PDF Universal Accessibility).

• Use Accessibility Checkers: Tools such as Adobe Acrobat Pro's Accessibility Checker or the free PAC 3 (PDF Accessibility Checker) can identify many common accessibility issues programmatically.
• Perform Manual Review with a Screen Reader: The most reliable validation method involves navigating the document using actual screen reader software (e.g., JAWS, NVDA, VoiceOver). This allows you to experience the document from an end-user's perspective.

Common Accessibility Pitfalls to Avoid

Adhering to these best practices ensures that your PDFs are not just visually appealing, but also semantically rich and fully accessible to all users, fostering inclusivity.

For quick online PDF accessibility tasks, from converting scanned documents to searchable text or managing document properties, PDFjin provides a suite of tools designed for efficiency and compliance.