\documentclass[a4paper]{scrartcl}
\usepackage{pdfpages}
\usepackage{graphicx}
\usepackage{tikz}
\typein[\pdfFile]{PDF-Datei:}
% alternativ:
%\def\pdfFile{Filename}
\unitlength1mm
\parindent0mm
\typearea{15}
\newcommand{\Grid}{
\thispagestyle{empty}
\hspace*{\fill}
\begin{tikzpicture}[line/.style={gray, thin}]
\foreach \y in {0, 0.5, ..., 23.5}
  \draw [line] (0,\y) -- (7,\y);
\foreach \x in {0, 0.5, ..., 7}
  \draw [line] (\x,0) -- (\x,23.5);
\end{tikzpicture}
}
\begin{document}
\clearpage
\includepdf[pages={1-},nup={1x3},frame=true,offset=-40mm 10mm,
delta=3ex 5ex,scale=0.75,
pagecommand={\Grid}]{\pdfFile}
\end{document}
