An Introduction to PDF Tags

What are PDF tags?

PDF tags are the key to accessing a PDF document’s content with assistive technologies such as screen readers. When a tagged PDF is created, each page element in the document is “tagged”. Each tag identifies the type of content and stores some attributes about it. They also arrange the document content into a hierarchical architecture (or a “tag tree”). The tag tree forms the logical structure of the document (reading order). The tag tree is comprised of the different tag types used within the document. Each document will have different tags depending on its content. Some examples are –Paragraphs, Headings, Lists, Tables, Figures, etc. 

Adding PDF tags does not change the visual appearance of the document; it provides invisible layer of formatting within the document that works with screen readers. PDF tags also allows the content to reflow seamlessly on devices with smaller screens, like smartphones and tablets.

Accessible document navigation

PDF Tags also provide efficient document navigation. Imagine reading a newspaper with no headlines? How would you choose which story to read? You would be stuck reading entire paragraphs of text before you could decide if the article was something you were interested in. PDFs with correctly tagged headings and subheadings provide a blueprint to the document content for those using assistive technology, similar the visual cues that a sighted person has when browsing documents.

Correct reading order

An accessible PDF provides the instructions to the assistive technologies such as screen readers to read the content properly and in the correct order. The tag order within the tag tree will determine the reading order of the document. For documents without this logical structure, the best case would be that assistive technologies would guess at the correct order that the content should be presented in. In worst cases, the content would be completely unable to be read. The outcome is that the content becomes useless to the user.

Accessible tables

Reading plain text is an easy task for assistive technologies. A table of data presents a complex more task. Proper PDF tag structure makes this possible by identifying essential information including the number of rows and columns as well as column (or row) headers, and which heading each data entry corresponds to. The more complex a table is, the more significant the challenge to tag it correctly.

Images (figures)

Figure tags include all kinds of non-text elements such as images, diagrams, infographics, logos, graphs, and charts. One attribute stored within a figure tag is the alt-text attribute (alternative text description).  An alt-text description provides a text description of the non-text element, so that users of assistive technologies receive the same relevant information that a sighted person receives. 

 Standardization

These days, content can be produced on any number of different authoring tools. Tagged PDF files that conform with the PDF/UA standard provide standardization of content. The PDF/UA standard ensures that assistive technologies and screen readers can correctly access the content within you documents, no matter which software tool you used to create it.

Tagging a document

This is often the most overwhelming part for someone who has been tasked to “make a document accessible”. The user must look at the existing content in a document and identify which tags to use to represent the existing content. To do this effectively requires a combination of design experience and knowledge of PDF tag structures.

It is possible to automatically add tags to a PDF using Adobe Acrobat, but the result is never satisfactory. Without careful, knowledgeable human inspection, testing and corrective actions (this process is called PDF remediation) the file will not meet the WCAG standards. Once the document is properly tagged and remediated, the document language and metadata settings need to be properly defined. Font size, font-embedding and color contrast will also need to be manually checked.

Proper remediation for PDFs needing to meet the WCAG 2.0 and PDF/UA standards requires specialized training.  PDF/UA files must meet 31 checkpoints with 136 failure conditions before they meet the ISO standard. Don’t worry, we are here to help. Contact us!