About tags, accessibility, reading order, and reflow

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. Thus tags can indicate the precise reading order and improve navigation—particularly for longer, more complex documents—without changing the appearance of the PDF.

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 and to 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.