Blur the whole document and add a demo watermark on each page

Question

This question is about blurring text but it is not about blurring everything in the document. This shows how to add the watermark over all pages (but it does not work with pictures, this shows how to do it with some extra star over pictures).

How can I blur the whole document and add a DEMO watermark on each page and possibly leave only one sentence without blurring?

Answer 1

Using Gonzalo's code with tikz

\documentclass{article}
\usepackage[printwatermark]{xwatermark}
\usepackage{xcolor}
\usepackage{tikz}
\usepackage{lipsum}

\newsavebox{\waterbox}
\begin{lrbox}{\waterbox}
\begin{tikzpicture}[remember picture]
 \fill[draw,white,opacity=0.7] ([shift={(2,2)}]current page.south west) rectangle (current page.north east);
 \node[text width = 2in,rotate=-45] at ([shift={(10mm,10mm)}]current page.center) {Some text here that appeas dark and rest is blurred};
\end{tikzpicture}
\end{lrbox}

\newwatermark*[allpages,angle=45,scale=3,xpos=0,ypos=0]{\usebox{\waterbox}}

\begin{document}

\lipsum[1-2]
\begin{figure}[!ht]
\centering
\includegraphics[width=3cm]{example-image-a}
\end{figure}
\lipsum[1-2]
\lipsum[1-20]
\end{document}

You have to adjust the position of text in

\node[text width = 2in,rotate=-45] at ([shift={(10mm,10mm)}]current page.center) {Some text here that appeas dark and rest is blurred};

Now with eso-pic.

\documentclass{article}
\usepackage{tikz}
\usepackage{lipsum}

\newsavebox{\waterbox}
\begin{lrbox}{\waterbox}
\begin{tikzpicture}[remember picture]
 \fill[draw,white,opacity=0.7] ([shift={(2,2)}]current page.south west) rectangle (current page.north east);
 \node[rotate=45,text width = 0.5\textwidth,scale=2,anchor=center,align=center] at ([shift={(0.6\paperwidth,1cm)}]current page.west) {Some text here that appeas dark and rest is blurred};
\end{tikzpicture}
\end{lrbox}

\usepackage{eso-pic}
\AddToShipoutPictureFG{%
\usebox{\waterbox}
}

\begin{document}

\lipsum[1-2]
\begin{figure}[!ht]
\centering
\includegraphics[width=3cm]{example-image-a}
\end{figure}
\lipsum[1-2]
\lipsum[1-20]
\end{document}

Answer 2

This method will work with fully text documents only, but will break down for documents that include images and/or \colorboxes.

The macro \blurpages{start page}{end page}{PDF file} takes a complete unblurred document as its 3rd argument.

It builds successive blurry images for each page of the specified page range by stacking shifted images atop each other. It then outputs the blurred page and continues through the page range.

In this MWE, I operate on the file xcolor.pdf, the documentation for the xcolor package.

\documentclass[a4paper]{article}
\usepackage{graphicx,ifthen,xcolor}
\usepackage[usestackEOL]{stackengine}
\usepackage{everypage}
% THESE ARE LaTeX DEFAULTS; CAN CHANGE IF NEEDED.
\def\PageTopMargin{1in}
\def\PageLeftMargin{1in}
\newcommand\atxy[3]{%
 \AddThispageHook{\smash{\hspace*{\dimexpr-\PageLeftMargin-\hoffset+#1\relax}%
  \raisebox{\dimexpr\PageTopMargin+\voffset-#2\relax}{\textcolor{red}{#3}}}}}
\newcommand\ateveryxy[3]{%
 \AddEverypageHook{\smash{\hspace*{\dimexpr-\PageLeftMargin-\hoffset+#1\relax}%
  \raisebox{\dimexpr\PageTopMargin+\voffset-#2\relax}{\textcolor{red}{#3}}}}}
% VERIFIED THAT SETTING \hoffset AND \voffset DO NOT BREAK SOLUTION.
%\hoffset=0.4in
%\voffset=0.2in
%WATERMARK ON EVERY PAGE
\ateveryxy{.5\paperwidth}{.55\paperheight}{\makebox[0pt]{\scalebox{15}{DEMO}}}
%CONSTRUCT BLURRED IMAGE
\setstackgap{L}{.4pt}
\newcommand\blur[2][1]{%
  \Longstack{%
    \,\includegraphics[page=#1,width=\paperwidth]{#2}\\
    \,\,\,\includegraphics[page=#1,width=\paperwidth]{#2}\\
    \includegraphics[page=#1,width=\paperwidth]{#2}\\
    \,\,\includegraphics[page=#1,width=\paperwidth]{#2}\\
    \,\,\,\,\includegraphics[page=#1,width=\paperwidth]{#2}
  }%
}
%PLACE BLURRED IMAGES ON SUCCEEDING PAGES
\newcounter{blurpage}
\newcommand\blurpages[3]{%
  \setcounter{blurpage}{#1}%
  \whiledo{\value{blurpage}<#2}{%
    \atxy{0in}{\paperheight}{\blur[\value{blurpage}]{#3}}\ \clearpage%
    \stepcounter{blurpage}%
  }%
  \atxy{0in}{\paperheight}{\blur[\value{blurpage}]{#3}}\ \clearpage%
}
\pagestyle{empty}
\begin{document}
\blurpages{1}{9}{xcolor}
\end{document}

Here is where the method breaks down, however: if there are color filled regions, including both images and \colorboxes.