PDF Accessibility
Understanding PDF Tags

Introduction

PDF Tags are a text-only representation of the PDF file which is hidden inside the PDF file which is presented to screen readers instead of the original file. They exist for accessibility purposes only and have no visible effect on the PDF file.

HTML tags and PDF tags often use similar tag names and organization structures, but they really are quite different. For one thing, it is impossible to insert PDF tags in a "code" view like you can with HTML. Still, if you are comfortable with HTML you will probably have an easier time creating and editing tagged PDF files.

If you have Acrobat 7 Professional, you may want to open it and practice features and techniques covered in the following article. An example of a tagged PDF: Section 508 Checklist.

Tags Tab

If you are following along, open the PDF in Acrobat Professional.

The Tags tab is the heart of tagged PDF files. You can view, reorder, rename, modify, delete and create tags within this panel. To view the tags, select View > Navigation Tabs > Tags. It may be easier to view the tags window if it is docked in the side bar. To do this, click View > Navigation Tabs > Dock all Tabs or drag the Tags tab into the side bar. For some reason, dragging the entire window will not cause it to dock. It must be dragged by the tab.

After expanding <Tags> and <Sect>, a long list of tags should be visible. The list can either be navigated by mouse or by keyboard. With a mouse, items can be expanded by clicking on the plus box next to the element. If an item is expanded, it can be collapsed by clicking on the minus box. Tags can also be collapsed and expanded using the left and right arrows. Navigation from element to element is possible using the up and down arrows.

Selecting a tag should highlight the corresponding content in the main window. If it does not, make sure Highlight Content is checked under the Options menu on the Tags tab.

Feel free to explore the Tags tab for a while before moving on.

After using the tags panel for a short time, you may have noticed a few of things:

• The interface can be a little confusing.
• The tags sometimes have different names than in HTML
• There seem to be additional tags for spaces, and other little things that shouldn't need tags.
• It can sometimes be a little hard to find which tag represents which element in the PDF.
• The tags don't seem as descriptive as in HTML.

Selecting a tag should highlight the text, image, or other element found inside it. If it does not, make sure Highlight Content is checked under the Options menu on the Tags tab.

It also may be more clear why it is preferable to start with a correctly formatted Word Document. Imagine creating an HTML document without any access to the code, where every change requires several mouse clicks, and you get a taste for how frustrating it is to create a tagged PDF from a poorly formatted document.

Find Tag From Selection

Just as selecting a tag highlights the content in the body of the PDF file, there is a way to accomplish the opposite effect of highlighting the tag that corresponds to selected content. First, click on the Select Tool . Select a portion of text, an image or a table and click on Options at the top of the Tags tab and then Find Tag From Selection from the dropdown list. This should highlight the appropriate tag.

Identifying Specific Tags

Many of the tags are similar, if not identical to HTML. Some of these familiar tags are described in the table below:

Although the previous table lists the tags recommended by Adobe, these are not always the tags used when a PDF file is created within another program. For example, a Microsoft Word document that is converted into a PDF file uses several unusual tags, such as <Heading 1> in place of <H1> or <InlineShape> instead of <Figure>. These tags are mapped to appropriate PDF tags using a technique called role mapping. You shouldn't have to modify the role map, but you can if you need to, by choosing Edit Role Map from the Options menu.

Run a Quick Check

Acrobat Professional includes two different Accessibility Checks. The first, the Quick Check, is not as helpful as it might sound. The Quick Check basically tells you whether the file has tags or not. It doesn't even identify the most basic errors, such as the missing alternate text. To run a Quick Check select Advanced > Accessibility > Quick Check.

Run an Advanced Check

The Advanced Check (Advanced > Accessibility > Full Check) is a more detailed version of the Quick Check. Although it is more complete than the Quick Check, it is far from complete. Still, it does identify features such as missing alternate text and offers hints on how to repair some errors.

Use Reflow

As with HTML, a screen reader will read a PDF document by the order of its tags, but the order of the tags in a PDF may not be the same as the reading visual order. This is especially likely if the PDF contains multiple columns or other blocks of text or complex nested lists. The Reflow Tool will reorder the visual order of the text based on the order of the tags.

To use the Reflow Tool, select View > Reflow or Ctrl + 4. If the document does not appear in the correct order while in Reflow, this is an indication that the order of the tags needs to be changed.