Where I can find the source code of pdflatex.exe?
This is quoted from the link given by @TH.
pdfTeX is built on top of TeX, written by Donald Knuth cum suis (Liang and so), and eTeX, written by Peter Breitenlohner cum suis; part of the paragraph optimization is inspired by the work of Hermann Zapf.
Does it imply that the source code of
pdflatex.exe will invoke