When you export to Adobe® PDF with the Create Tagged PDF option selected in the General area of the Export Adobe PDF dialog box, the exported pages are automatically tagged with a set of structure tags that describe the content, identifying page items such as headlines, stories, and figures. To add more tags or to fine-tune existing ones before you export, you can use the Tags panel in Adobe InDesign® software. The Structure pane (View > Structure > Show Structure) reflects the changes.
You can improve the accessibility and reuse of Adobe PDF documents by adding tags to the InDesign document before you export. If your PDF documents don't contain tags, Adobe Reader® or Acrobat® software may attempt to automatically tag the document when the user reads or reflows it, but the results may be disappointing. If you do not get the results you want in the exported PDF file, you can use tools in Acrobat 6.0 Professional and later to edit the structure of tagged PDF documents. For the most advanced tools, use Acrobat 9 Professional.
When you apply tags to a document for PDF export, the tags do not control which content is exported to PDF, as is the case with XML export. Instead, the tags give Acrobat more information about the document's structural contents.
Advantages of using tags
By applying tags to your document before exporting to PDF, you can do the following:
- Map InDesign paragraph style names to Acrobat tagged Adobe PDF paragraph styles to create a reflowable PDF file for viewing on handheld devices and other media.
- Mark and hide printing artifacts, text, and images so that they won't appear when reflowed in Acrobat. For example, if you tag a page item as Artifact, the page item will not be displayed when you reflow the contents of a tagged Adobe PDF document on a handheld device, a small display, or a monitor at a large magnification.
- Add alternative text to figures so that the text can be read aloud to the visually impaired with screen-reading software.
- Replace graphic letters, such as ornate drop caps, with readable letters.
- Provide a title for a set of articles, or group stories and figures into articles.
- Order stories and figures to establish a reading order.
- Recognize tables, formatted lists, and tables of contents. Recognize which content blocks belong to the different stories.
Include text formatting information such as Unicode values of characters, spacing between words, and the recognition of soft and hard hyphens.
How Tags Affect Reuse and Accessibility
The content of an 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 subsections. 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 9 Professional. For more information, see Acrobat Help.
