The linked instructions cover PDF/A-1b (have plain text version of contents), but Tagged PDF is more than that -- it's about encoding the structure of the document.

There is a POC package for producing Tagged PDF here https://github.com/AndyClifton/accessibility but it's not a complete solution yet.

Here is an excellent review article that talks about all the other options for producing Tagged PDFs from LaTeX (spoiler — there is no solution currently): https://umij.wordpress.com/2016/08/11/the-sad-state-of-pdf-a... via https://news.ycombinator.com/item?id=24444427