The following example centers an image in the text area of a new page. The image is maximized without distortion:
\documentclass{article}
\usepackage{graphicx}
\newcommand*{\IncludePageImage}[2][]{%
\newpage
\begingroup
\centering
\setlength{\parskip}{0pt}%
\setlength{\topskip}{0pt}%
\nointerlineskip
\vspace*{\fill}%
\includegraphics[%
width=\textwidth,
height=\textheight,
keepaspectratio,
#1%
]{#2}%
\par
\vspace*{\fill}%
\newpage
\endgroup
}
\begin{document}
\IncludePageImage{file.pdf}
\end{document}
The page layout can be made visible by option showframe of package geometry:
\usepackage[pass,showframe]{geometry}
Option pass is useful, if the layout is defined without package geometry. Then package geometry lets the layout parameter untouched if option pass is given.
\includepdf;\includegraphicsis sufficient and it wouldn't override the page style. – egreg Jan 27 '14 at 22:30