Adobe 22020807 Accessibility Guide - Page 6

2 | Introduction reliably, independently of the environment in which they were created. PDF relies on the same imaging model as the PostScript® page description language to describe text and graphics in a device-independent and resolution-independent manner. To improve performance for interactive viewing, PDF defines a more structured format than that used by most PostScript language programs. PDF also includes objects, such as annotations and hypertext links, that are not part of the page itself but are useful for interactive viewing and document interchange. Accessible PDFs have the following characteristics: Searchable text 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 software cannot read or extract the words in a graphic representation, users cannot select or edit the text, and you cannot manipulate the PDF for accessibility. You must convert the scanned images of text to searchable text using optical character recognition (OCR) before you can use other accessibility features with the document. Fonts that allow characters to be extracted to text 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 printer. This extraction fails if Acrobat cannot determine how to map the font to Unicode characters. Interactive form fields Some PDFs contain forms that a person is to fill out using a computer. To be accessible, form fields must be interactive-meaning that a user must be able to enter values into the form fields. Interactive PDF forms also have a defined tab order allowing users of assistive technology to use the tab key in order to progress from one form field or interactive control in a logical manner. Refer to the document Adobe® Acrobat® 9 Pro Accessibility Guide: Creating Accessible Forms for complete details. Other Interactive Features: Buttons, hyperlinks, and navigational aids 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. Many of these aids can be accessed using the keyboard without relying on the mouse. Document language Specifying the document language in a PDF enables some screen readers to switch to the appropriate language. Security that will not interfere with assistive technology Some authors of PDFs restrict users from printing, copying, extracting, adding comments to, 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 a screen reader's ability to convert the on-screen text to speech. Document structure tags and proper read order To read a document's text and present it in a way that makes sense to the user, a screen reader or other textto-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. Alternative text descriptions Document features such as images and interactive form fields can't be read by a screen reader unless they have associated alternative text. Though web links are read by screen readers, you can provide more Adobe Acrobat 9 and PDF Accessibility