Button in the bottom of all pages to return back to table of content

The following might get you started. Just replace example-image with an image file of your button:

documentclass{article}
usepackage{blindtext} % just for dummy contents
usepackage{tikz}
usepackage{eso-pic}

usepackage{hyperref}

begin{document}
 AddToShipoutPicture{%
begin{tikzpicture}[remember picture,overlay]
 node [rectangle, anchor=center, yshift=2cm] 
 (boxthepage) at 
 (current page.south){hyperlink{mytableofcontents}{includegraphics[width=1cm]{example-image}}};
end{tikzpicture}}

phantomsection 
hypertarget{mytableofcontents}{}
tableofcontents

blinddocument

end{document}