|Document Structure Tags and Proper Reading Order
To read a document’s text and present it in a way that makes sense, a screen reader or other text-to-speech tool requires that the document be structured. Document structure tags in a PDF define the reading order and identify headings, paragraphs, sections, tables and other page elements.
|Document Language and Title Indication
Specifying the document language in a PDF enables some screen readers to switch the current speech synthesizer to the appropriate language. This allows for correct pronunciation of content in different languages. Providing a document title allows the user to locate and identify the document.
A document that consists of scanned images of text is inherently inaccessible because the content of the document is a graphic representing the letters on the page, not searchable text. This must be converted into searchable text using optical character recognition (OCR).
|Navigational aids in a PDF
Navigational aids such as links, bookmarks, headings, a table of contents, and a preset tab order for form fields — assist all users in using the document. Bookmarks are especially useful and can be created from document headings. These features can be accessed using the keyboard without relying on the mouse which allows for multiple ways for users to navigate content.
|Interactive Labeled Form Fields
Some PDFs contain interactive forms that people fill out using a computer. To be accessible, form fields must be interactive; that is, a user must be able to enter values into the form fields. Forms must provide identification, give tips on proper completion, and prevent errors. Form entry should not be timed unless the user can request more time.
|Alternative Text Descriptions for Non-Text Elements
Document features such as images and interactive form fields cannot be understood by the user of a screen reader unless they have associated alternative text. Though link text is available to screen reader users, it is possible to provide more meaningful descriptions via replacement text. Alternative text for images and tooltips can aid many users.
|Fonts that allow Characters to be Extracted to Text
The fonts in an accessible PDF must contain enough information for purposes other than displaying text on the screen. This is typically done by extracting the font to Unicode text.
What it Takes to be Compliant
Characteristics of Accessible PDF Documents
PDF files are created in a variety of ways, from a variety of applications, and for a variety of purposes. Achieving the desired accessibility goals for an individual PDF file requires understanding the nature of the PDF and its intended use. A document is considered accessible if it meets certain technical criteria and can be used by people with disabilities. This includes access by people who are mobility impaired, blind, low vision, deaf, hard of hearing, or who have cognitive impairments.