\documentclass[french]{article}

\usepackage{headers}

\begin{document}

\include{parts/title}

\setcounter{tocdepth}{3}
\tableofcontents

\pagebreak
\sffamily
\input{parts/introduction}
\input{parts/part1}
\input{parts/part2}
\input{parts/part3}
\input{parts/part4}

\end{document}