The content of a Adobe PDF document can be reused for other purposes. For example, you might create an Adobe PDF file of a report with text, tables, and images, and then use various formats to distribute it: for printing or reading on a full-sized monitor, for viewing on a handheld device, for reading out loud by a screen reader, and for direct access through a web browser as HTML pages. The ease and reliability with which you can reuse the content depends on the underlying logical structure of the document.

To make sure that your Adobe PDF documents can be reused and accessed reliably, you must add tags to them. Tagging adds an underlying organizational structure, or logical structure tree, to the document. The logical structure tree refers to the organization of the document’s content, such as title page, chapters, sections, and subsection. It can indicate the precise reading order and improve navigation—particularly for longer, more complex documents—without changing the appearance of the PDF document.

For people who are not able to see or decode the visual appearance of documents, assistive technology can access the content of the document reliably by using the logical structure tree. Most assistive technology depends on this structure to convey the meaning of content and images in an alternative format, such as sound. In an untagged document, no such structure exists, and Acrobat must infer a structure, based on the reading order choices in the preferences. This method is unreliable and often results in page items read in the wrong order or not read at all.

The tags appear on the Tags tab in Acrobat 6.0 and later, where they are nested according to the relationship definitions for the tagged elements. You cannot edit tags in Acrobat Standard. If your work requires you to work directly with tags, you should upgrade to Acrobat 8 Professional. For more information, see Acrobat Help.

Logical structure tree on the Tags tab in Acrobat 8