booklet.tex

\documentclass[a4paper]{article}
\usepackage{pdfpages}
\usepackage{lastpage}
\begin{document}
	\includepdf[pages=-,booklet,landscape]{main.pdf}
	
	
	% the logic below needs to be thoroughly checked
	
	% To make sure that the first page includes both, the front and back cover,
	% we process the first and last page
	%\includepdf[pages={1,last}, nup=1x2, landscape=false, angle=90]{main.pdf}

	% Then we add the rest of the document, skipping the first and last pages.
	% But first, we have to get the total number of pages and figure out what
	% the number of the "last but one" page is.
	%\edef\TotalPages{\the\pdflastximagepages}
	%\edef\SecondToLastPage{\the\numexpr\TotalPages-1}

	% Add the rest
	%\includepdf[pages=2-\SecondToLastPage, booklet, landscape]{main.pdf}

\end{document}