\documentclass{article}
\usepackage{docassembly}
\usepackage{lipsum}

\hypersetup{pdfpagemode=UseNone}

% Look in the Adobe Acrobat JavaScript manual under the addWatermarkFromFile to see all the possible parameters.
\begin{docassembly}
\retnAbsPathAs(_path);
_path += "/graphics/AeB_Logo.pdf";
\addWatermarkFromFile({
    bOnTop:false,
    bOnPrint:false,
    nOpacity: 0.2,
    nRotation: 90,
    cDIPath:_path
});
\executeSave();
\end{docassembly}

\begin{document}

\lipsum[1-30]

\end{document}