Improving PDF File Accessibility
Traditional documents contain several items that can present accessibility barriers, including images, charts and tables. Almost all of what is presented in a document is visual, and therefore can present difficulties for individuals with vision disabilities. While there are document formats that can contain sound, it is beyond the scope of this module. Keep in mind that spoken audio needs to be transcribed.
A key element of Adobe Reader is the ability to expose elements to screen readers. A screen reader is a piece of software that reads content via a synthesized voice. Previous versions of Adobe Reader were not able to expose elements to screen readers, thereby making the document inaccessible to these users.
Though several of the previous accessibility issues have been automated, the main issue now lies on the shoulders of the document designer, who must have a good idea of how the document is to be structured. The general idea is that not only should you expose the content of the document, but meta information such as its layout and reading order as well.
Checking the structure of the PDF
Defined structure is an important accessibility requirement of PDF files. A well-defined structure is used by assistive technologies to help deliver content in a meaningful, organized way. Without structure, the PDF content cannot be reorganized to fit the size of the viewing window and screen readers will have difficulty interpreting certain layout elements such as multiple columns or embedded tables. However, by identifying which text is a header and which is a paragraph, the PDF file becomes logically structured and facilitates the creation of a tagged (accessible) PDF file. Both Adobe Acrobat and Adobe Reader provide a mechanism for checking the structure and accessibility of a PDF file, and Adobe Acrobat provides tools to add in this structure to existing documents.
Creating Text Equivalents
Another important concept in accessibility is providing alternative text for images. Much like how structuring your document provides key information regarding the layout, alternative text provides a short description of an image. It is only necessary to provide an overview of what the image is if it provides important contextual information. For example if a document contained a picture of stars in space, that may be relevant if the document is talking about astronomy topics. This would be less important if the image was used as a background.
Define Language of PDF File
It is also important to define the language of the document. If the document language is not specified, it will be brought to your attention when using the accessibility checker.
To define the language of a document in Adobe Acrobat 8:
- Under the 'File' menu choose 'Properties' or right-click the current page and choose ‘Document Properties’.
- Click on the ‘Advanced’ tab.
- At the bottom of the window is a pull-down menu titled ‘Language’. Select the appropriate language and click ‘OK’.
Forms
Forms allow users to fill out information electronically, and often include common components such as text fields and radio buttons. The form can then be submitted electronically. Many government institutions are now in the process of converting their current paper-based system to an electronic system. Since Adobe Acrobat is an excellent tool for creating forms, you will more than likely run into a time that you will need to make form elements accessible. Form elements can present accessibility barriers in much the same way that images can. By default, form elements can not be seen by screen readers, thus making the form inaccessible for people with certain disabilities.
When working with forms, it is necessary to insert the form element into the tag hierarchy, and to give it a valid name. Doing so exposes the name of the element to the screen reader, allowing it to be read correctly. Keep in mind that providing names for elements is insufficient on its own. You must also remember to structure all document elements appropriately.
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