-c HTML_PAGE_FOOTER= I'm not sure if it will solve your case, but FWIW, we used -c PRE_BODY_CLOSE for this purpose for an unofficial LaTeX manual I contribute to. Here is one of its intro pages so you can see the result: http://latexref.xyz/About-this-document.html
The <hr> and link at bottom were added by us, via this option: -c PRE_BODY_CLOSE="<hr/><div class='referenceinfo'>\ <a href='https://latexref.xyz/'>\ <i>Unofficial LaTeX2e reference manual</i></a></div>" Best, Karl
