I have been having problems since ever when trying to distribute some content to people and keeping track of the NDAs I make them sign. A sound solution (good but not really impossible to break) is to watermark the documents before sending. Then if you detect it in the wrong hands, you can ate least trace who did it.
I had for a long time a code to do this, but the real problem was that this code was actually in TeX, meaning that to make it appear in a PDF I have to convert from dvi to ps and then to pdf. I real pain, plus you finish loosing all the goodies from pdflatex, in term of hyperref.
I found a site[1], and with his instructions I managed to produce my own code to put the copyright watermark in my pdflatex documents, here it is:
\usepackage{graphicx,type1cm,eso-pic,color}
\makeatletter
\AddToShipoutPicture{%
\setlength{\@tempdimb}{.5\paperwidth}%
\setlength{\@tempdimc}{.5\paperheight}%
\setlength{\unitlength}{1pt}%
\put(\strip@pt\@tempdimb,\strip@pt\@tempdimc){%
\makebox(0,0){\rotatebox{45}{\textcolor[gray]{0.95}%
{\fontsize{3cm}{3cm}\selectfont{Final Version}}}}%
\makebox(-100,-300){\rotatebox{45}{\textcolor[gray]{0.95}%
{\fontsize{2cm}{2cm}\selectfont{Internal Use}}}}
\makebox(-500,-0){\rotatebox{90}{\textcolor[gray]{0.95}%
{\fontsize{0.7cm}{0.7cm}\selectfont{\textcopyright Copyright 2008 - Jean Martina}}}}
}%
}
\makeatother
You should put this code in your preamble, and it will put a watermark in all your pages. You can change the texts and their positions quite easily, just try it.
[1]- http://filoxus.blogspot.com/2008/01/how-to-insert-watermark-in-latex.html