\documentclass{article}
\usepackage{amsmath}
\usepackage[active,tightpage]{preview}
\setlength\PreviewBorder{1pt}
\usepackage{pgf}
\usepackage{tikz}
\usepgfmodule{plot}
\usepgflibrary{plothandlers}
\usetikzlibrary{shapes.geometric}
\usetikzlibrary{shadings}
\usepackage{graphicx}
\author{Author}
\title{How to include images in a \LaTeX\ document}
\date{June, 2013}
\begin{document}
\begin{preview}
\maketitle
Using the pdf file:

\begin{center}
        \includegraphics[width=0.80\textwidth]{../images/pic_for_complete_document.pdf}
\end{center}

Using the PGF/TikZ code:

\begin{center}
\input{../images/tikz_pic_for_complete_document.tex}
\end{center}
If you want to scale this image, please chang the ``scale'' in the file
\texttt{tikz\_pic\_for\_complete\_document.tex} 
\end{preview}
\end{document}
