trans.tex

\documentclass{article}
\usepackage{lipsum}

\usepackage{graphicx}
\usepackage{transparent}
\usepackage{eso-pic}
\AddToShipoutPicture*{
    \put(0,0){
        \parbox[b][\paperheight]{\paperwidth}{%
            \vfill
            \centering
            {\transparent{1}\includegraphics[width=1\textwidth]{theta2.pdf}}%
            \vfill
        }
    }
}

\begin{document}
\lipsum
\end{document}