A document or application is accessible if people with disabilities, such as mobility impairments, blindness, and low vision, can use it. Accessibility features in Acrobat, Acrobat Reader, and Adobe Portable Document Format (PDF) enable people with disabilities to use PDF documents, with or without screen readers, screen magnifiers, and braille printers.
Making PDFs accessible tends to benefit all users. For example, the document structure that enables a screen reader to read a PDF out loud also enables a mobile device to reflow and display the document on a small screen. Similarly, the preset tab order of an accessible PDF form helps all users, not just users with mobility impairments, fill the form more easily.
Accessibility features in Acrobat and Acrobat Reader fall into two broad categories. There are features to make the reading of PDF documents more accessible, and features to create accessible PDF documents. To create accessible PDF documents, use Acrobat, not Reader.
- Preferences and commands to optimize output for assistive software and devices, such as saving as accessible text for a braille printer
- Preferences and commands to make navigation of PDFs more accessible, such as automatic scrolling and opening PDFs to the last page read
- Accessibility Setup Assistant for easy setting of most preferences related to accessibility
- Keyboard alternates to mouse actions
- Reflow capability to display PDF text in large type and to temporarily present a multicolumn PDF in a single, easy-to-read column.
- Read Out Loud text-to-speech conversion
- Support for screen readers and screen magnifiers
- Creation of tagged PDFs from authoring applications
- Conversion of untagged PDFs to tagged PDFs
- Security setting that allows screen readers to access text while preventing users from copying, printing, editing, and extracting text
- Ability to add text to scanned pages to improve accessibility
- (Acrobat Pro) Tools for editing reading order and document structure
- (Acrobat Pro) Tools for creating accessible PDF forms
Acrobat Standard provides some functionality for making existing PDFs accessible. Acrobat Pro enables you to perform tasks, such as editing reading order, or editing document structure tags that are necessary to make some PDF documents and forms accessible.
A document that consists of scanned images of text is inherently inaccessible because the content of the document is images, not searchable text. Assistive software cannot read or extract the words, users cannot select or edit the text, and you cannot manipulate the PDF for accessibility. Convert the scanned images of text to searchable text using optical character recognition (OCR) before you can use other accessibility features with the document.
Screen readers cannot read document features such as images and interactive form fields unless they have associated alternate text. Screen readers can read web links; however, you can provide more meaningful descriptions as alternate text. Alternate text and tool tips can aid many users, including users with learning disabilities.
The fonts in an accessible PDF must contain enough information for Acrobat to 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 feature. Acrobat also extracts characters to Unicode when you save as text for a braille printer. This extraction fails if Acrobat cannot determine how to map the font to Unicode characters.
To read a document’s text and present it in a way that makes sense to the user, a screen reader or other text-to-speech tool requires a structured document. Document structure tags in a PDF define the reading order and identify headings, paragraphs, sections, tables, and other page elements.
Some PDFs contain forms that a person is to fill out using a computer. To be accessible, form fields must be interactive to let the user enter values into the form fields.
Navigational aids in a PDF include links, bookmarks, headings, table of contents, and preset tab order for form fields. Navigational aids assist users in understanding the document without reading completely through it. Bookmarks are especially useful and can be created from document headings.
Specifying the document language in a PDF enables some screen readers to switch to the appropriate language.
Some PDF authors restrict users from printing, copying, extracting, adding comments, or editing text. The text of an accessible PDF must be available to a screen reader. You can use Acrobat to ensure that security settings don’t interfere with the screen reader’s ability to convert onscreen text to speech.
For more information about PDF accessibility, see www.webaim.org/techniques/acrobat/.
PDF tags are similar in many ways to XML tags. PDF tags indicate document structure: which text is a heading, which content makes up a section, which text is a bookmark, and so on. A logical structure tree of tags represents the organizational structure of the document. Therefore, tags indicate the reading order and improve navigation, particularly for long, complex documents without changing the PDF appearance.
Assistive software determines how to present and interpret the content of the document by using the logical structure tree. Most assistive software depends on document structure tags to determine the appropriate reading order of text. Document structure tags let assistive software convey the meaning of images and other content in an alternate format, such as sound. An untagged document does not have structure information, and Acrobat must infer a structure based on the Reading Order preference setting. This situation often results in page items being read in the wrong order or not at all.
Reflowing a document for viewing on the small screen of a mobile device relies on these same document structure tags.
Often, Acrobat tags PDFs when you create them. To determine whether a PDF contains tags, choose File > Properties, and look at the Tagged PDF value in the Advanced pane of the Description tab.
In Acrobat Pro, the logical structure tree appears on the Tags panel. It shows document content as page elements nested at various levels.