What is pdfTeX?
One can reasonably say that pdfTeX is (today) the main stream of TeX distributions: most LaTeX nowadays use pdfTeX whether they know it or not.
pdfTeX is a development of TeX that is capable of generating typeset PDF output in place of DVI. pdfTeX has other capabilities, most notably in the area of fine typographic detail (for example, its support for [optimising line breaks](FAQ-overfull)), but its greatest impact to date has been in the area of PDF output.
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