\documentclass{article}

\usepackage[utf8]{inputenc}
\usepackage[T1]{fontenc}
\usepackage{amsmath, amsfonts, amssymb, amsthm}
\usepackage{tikz}

\author{Debucquoy Anthony}
\title{Extension messagerie}

\begin{document}

\section{Use case diagram}

\begin{center}
\resizebox{390pt}{!}{
	\input{./use_case_messagerie.tex}
}
\end{center}

\subsection{Answer topic}
\subsection{Create discutions}
\subsubsection{Send messages}
\subsection{Ask apointment}
\subsubsection{Export to calendar}
\subsection{Manage apointment}
\subsubsection{Propose new apointment}
\subsection{Create forum}
\subsubsection{Post topics}
\subsubsection{Post poll}

\end{document}