Characteristics of Accessible PDF Files

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Accessible PDFs include but are not limited to the following characteristics:

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.

Assistive technology software cannot read or extract the words in a graphical representation. Furthermore, users cannot select or edit the text or manipulate the PDF for accessibility. Scanned images of text must be converted into to searchable text using optical character recognition (OCR) before addressing accessibility in the document.

Here is an example of a PDF that does not have searchable text and is an image. Download PDF that does not have searchable text and is an image.

 

 

 

 

 

 

The fonts in an accessible PDF must contain enough information for Acrobat to correctly extract all of the characters to text for purposes other than displaying text on the screen. Acrobat extracts characters to Unicode text when you read a PDF with a screen reader or the Read Out Loud tool, or when you save as text for a Braille embosser. This extraction fails if Acrobat cannot determine how to map the font to Unicode characters.

 

 

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.

 

 

 

 

 

 

 

 

Navigational aids in a PDF — such as links, bookmarks, headings, a table of contents, and a preset tab order for form fields — assist all users in using the document without having to read through the entire document, word by word. Bookmarks are especially useful and can be created from document headings. These features can be accessed using the keyboard without relying on the mouse, and allow for multiple ways for users to navigation content.

 

Specifying the document language in a PDF enables some screen readers to switch the current speech synthesizer to the appropriate language, allowing correct pronunciation of content in different languages. Providing a document title allows the user to locate and identify the document.

Security that will not Interfere with Assistive Technology

Some authors of PDFs restrict users from printing, copying, extracting, editing or adding comments to text. The text of an accessible PDF must be available to a screen reader. Acrobat’s security settings can be set to protect document content while not interfering with a screen reader’s ability to convert the on-screen text to speech or Braille.

 

PDFs need correctly structured tags as screen readers or other assistive technologies determine information like reading order and interpreting the document based on the tags panel. 

PDF tags the reading order and identify headings, paragraphs, sections, tables, and other page elements.

The tags structure also allows for documents to be resized and reflowed for viewing at larger sizes and on mobile devices.

 

 

 

 

 

 

 

 

 

 

 

 

 

The user of a screen reader can not understand document features such as images and interactive form fields unless they have associated alternative text.

Though link text is available to screen reader users, it is possible to provide more meaningful descriptions via actual text. Alternative text for images and tooltips can aid many users including those with learning disabilities.

Accessible equivalents for multimedia, including any audio and video elements, must also be present.

 

 

 

 

 

 

 

There are additional characteristics of accessible documents including:

• No reliance on color or sensory characteristics alone to convey meaning.
• Use of color combinations that provides a sufficient degree of contrast.
• Controls for audio.
• Use of text instead of images of text.
• No use of flashing or blinking elements.
• No focus changes without user initiation.
• Consistent navigation and identification of elements.