\documentclass[pdftex, a4paper, 11pt]{book}
\usepackage[left = 3cm, right = 3cm, top = 2.5cm, bottom = 2.5cm]{geometry}
\usepackage[bookmarks, colorlinks, plainpages=false, pdfpagelabels]{hyperref}
\usepackage[pdftex]{graphicx}
\makeatletter
\renewcommand\paragraph{\@startsection{paragraph}{4}{\z@}%
                                    {-3.25ex \@plus-1ex \@minus-.2ex}%
                                    {0.5ex \@plus0.2ex}%
                                    {\normalfont\large\bfseries}}
\makeatother
\title{My Book}
\author{Milarepa}
\begin{document}
\frontmatter
\maketitle
\tableofcontents
\mainmatter
% H E R E  B E G I N S  Y O U R  D O C U M E N T
% Here is a Reference Example ~    te{example}
\backmatter
\addcontentsline{toc}{section}{Bibliography}
\begin{thebibliography}{99}
\bibitem{example} This is an example
\end{thebibliography}
\end{document}