\documentclass{article}
\usepackage{pdfpages}
\usepackage{tikz}

\newcommand\Watermark{%
  \begin{tikzpicture}[remember picture,overlay]
    \node[
      rotate=45,
      scale=12,
      text=red,
      opacity=0.2
    ] at (current page.center) {\bfseries Sample};
  \end{tikzpicture}%
}

\begin{document}

\includepdf[
  pages=1,
  pagecommand={\Watermark}
]{CSWCCL.pdf}

\end{document}