PDF/Universal Access (PDF/UA) is an International Organization for Standardization (ISO) standard for accessible PDF technology. A technical specification intended for developers implementing PDF writing and processing software, PDF/UA provides definitive terms and requirements for accessibility in PDF documents and applications. For those equipped with appropriate software, conformance with PDF/UA ensures accessibility for people with disabilities who use assistive technology such as screen readers, screen magnifiers, joysticks and other technologies to navigate and read electronic content.
- PDF is primarily a graphical language developed to show printable pages on electronic devices and print consistently on a wide range of printers.
- PDF have basically three layers of information:
- Graphical layer that defines visual rendering of the page content.
- Text layer to make PDF documents searchable using plain text searches.
- A tagging layer that represents the content of the text and graphical layers to assistive technologies, with most tags similar to HTML element names.
- Many PDF documents only have the graphical layer defined.
- Only documents with the tagging layer (e.g. Tagged PDF) are considered accessible.
- Most PDF creation tools do not provide a tagging layer, so adding the layer must be done manually after creation. This can be a time consuming process for large or complex documents.
- PDF readers like Adobe Acrobat reader will automatically create a text and tagging layer for PDF documents using optical character recognition. The accuracy of the tag PDF document will vary greatly depending on the complexity and quality of the document. This feature may make a PDF document that isn’t tagged look accessible to assistive technology users.