The file format PDF is an ISO standard. The newest version is ISO 32000-1:2008 which is based upon PDF 1.7. The standard is described in the PDF specification, 756 pages full of technical speech. There you can read
- which PDF standard tags are available
- how to use them and
- some more issues concerning tagged PDF.
- Adobe offers an ISO approved copy of the ISO 32000-1 Standards document as a free version: http://wwwimages.adobe.com/www.adobe.com/content/dam/Adobe/en/devnet/pdf/pdfs/PDF32000_2008.pdf