LaTeX Watermark

\documentclass{article}
\usepackage{tikz}
\usepackage{pdfpages}
\usepackage[utf8]{inputenc}
\usepackage[english,russian]{babel}
\pagestyle{empty}
\newcommand{\filename}{path/to/some/pdf/file.pdf}
\newcommand*\watermarktext[1]{\leavevmode\hbox to 6\textwidth{\leaders\vbox to 4\textheight{\leaders\hbox{#1}\vfil}\hfil}}

\newcommand{\watermark}{\tikz[remember picture, overlay]
 \node [black,opacity=0.1,rotate=45,scale=1.3] at (current page.center)
   {\watermarktext{some watermark text here }};}

\begin{document}
\foreach \index in {1,...,\the\pdflastximagepages}
{
\includepdf[pages=\index,pagecommand={\watermark}]{\filename}
}
\end{document}