\documentclass{article}

\usepackage[printwatermark=true ,color=gray!35 ,textmark={mark} ,angle=-30 ,xcoord=10mm ,ycoord=100mm]{xwatermark}

\usepackage{xepersian}
\settextfont[Scale=1]{XB Zar}
\setlatintextfont[Scale=.8]{Linux Libertine}

\begin{document}
This is test.
\end{document}