The computer program pdfTeX is an extension of Knuth's typesetting program TeX, and was originally written and developed into a publicly usable product by Hàn Thế Thành as a part of the work for his PhD thesis at the Faculty of Informatics, Masaryk University, Brno, Czech Republic.

Knuth later met Hàn Thế Thành in Brno during his visit to the Faculty of Informatics to receive an honorary doctorate from Masaryk University.

Two prominent characteristics of pdfTeX are character protrusion, which generalizes the concept of hanging punctuation, and font expansion, an implementation of Hermann Zapf's ideas for improving the grayness of a typeset page.

This allows tight integration of PDF features such as hypertext links and tables of contents, using packages such as hyperref.

On the other hand, packages (such as PSTricks) which exploit the earlier conversion process of DVI-to-PostScript may fail, although replacements such as PGF/TikZ have been written.