Headings divide your content into meaningful sections. Heading tags (H1, H2, H3, etc.) help provide structure by indicating which of your headings should be subordinate to which. Likewise, each block of text (tagged ‘”P” for paragraph) in your document must be individually tagged so that you can assign it a place in the page’s reading order. If your document’s headings and text are tagged incorrectly, you can fix them using the Touch Up Reading Order tool.
If your document seems "close" to the logical structure, you may want to keep what is there so far and edit/add to it.
If your PDF document does not contain tags, or many are incorrect you will want to to select Clear Page Structure to clear the document. This function is a page by page function, therefore you will need to repeat it on each page of your document.
After selecting Structure Types in the Touch Up Reading Order panel, items that have identifiers on them (tags) will show the structure.
The following screenshot gives an example of what you may see. In this example, some elements are tagged and others are not; some are tagged correctly, and others are not. This is frequently the case when documents are made accessible incorrectly (or not at all) in their native software.
Incorrect elements identified include:
The Touch Up Reading Order tool allows you to see if your document’s headings, images, and decorative background elements are properly “tagged” (that is, marked such that Adobe Acrobat can recognize them correctly).
Opening the Touch Up Reading Order tool
From the the toolbar at the top right, select Tools, Accessibility, then Touch Up Reading Order
An accessible document is required to have a title and primary language established.
These streamlined instructions are intended for use with relatively simple documents that require only basic accessibility formatting (e.g.. your document consists of only a few pages with a basic heading structure, a few simple images, no special requirements for security, interactivity, or language, etc.). For more complicated documents or for more detailed instructions, see Adobe’s Acrobat Accessibility Training Resources at adobe.com.
PDF files are created in various ways. In the past, documents would be scanned, saved as image files, then converted to PDF. Upgrades in scanning software have helped to curtail this result, but it still happens. If scanning a document that contains text, be sure to always select the option that provides for OCR results. Scanning software may provide an OCR choice or similar such as "text", "text and graphics", "document", or other description option.
For a PDF to be accessible it must contain a tag structure. This structure allows for Assistive Technology such as screen readers and refreshable Braille readers to identify page elements such as headings, lists, paragraphs, and form elements. Aside from just reporting if a PDF contains tags, one must check that the tag structure makes logical sense with the reading order of the document.