\documentclass[11pt]{lettre}
\usepackage[latin1]{inputenc}
\usepackage[T1]{fontenc}
\usepackage[frenchstyle]{kpfonts}
\usepackage[frenchb]{babel}


\begin{document}
\institut{pp_adresse}
\begin{letter}{a}
\signature{a}
\opening{Madame, Monsieur,}

a

\closing{Veuillez agréer, Madame, Monsieur, l'expression de mes salutations distinguées.}
%\cc{Cclist}
%\ps{adding a postscript}
%\encl{list of enclosed material}
\end{letter}
\end{document}