PDF's logical structure features (introduced in PDF 1.3) provide a PDF/UA also specifies the rules governing the behavior for a conforming reader.
The mechanisms for including the components in the PDF stream are left to the discretion of the individual developer, PDF generator, or PDF viewing agent. The specification describes the required and prohibited components and the conditions governing their inclusion in or exclusion from a PDF file in order for the file to be available to the widest possible audience, including those with disabilities. Of note for accessibility is PDF/UA (Universal Accessibility) which became an ISO Standard in July 2012 (ISO 14289-1:2012 (See PDF/UA (ISO 14289-1:2012).) The scope of PDF/UA is not meant to be a techniques (how-to) specification, but rather a set of guidelines for creating more accessible PDF.
In January 2008, PDF 1.7 became an ISO standard (ISO 32000-1). The PDF specification was introduced by Adobe Systems in 1993 as a publicly available standard. PDF files specify the appearance of pages in a document in a reliable, device-independent manner. The Portable Document Format (PDF) is a file format for representing documents in a manner independent of the application software, hardware, and operating system used to create them, as well as of the output device on which they are to be displayed or printed.
