\documentclass[a4paper,landscape]{article}
\usepackage{geometry}

\pagestyle{empty}

\usepackage{xparse}
\usepackage{graphicx}
\usepackage{tikz}
\usetikzlibrary{calc}
\tikzset{
	every node/.style = {
		inner sep = 0pt,
		anchor = north west,
	}
}

\ExplSyntaxOn

\int_new:N \l_impose_repetitions_int
\int_new:N \l_impose_counter_int
\dim_new:N \l_impose_creep_dim
\int_new:N \l_impose_total_pages_int
\int_new:N \l_impose_total_pages_to_four_int

\cs_new:Npn \impose_get_page:nn #1#2 {
	\int_compare:nT { ( #1 ) <= \l_impose_total_pages_int } {
		\includegraphics [
		width = 0.5\paperwidth,
		page = #1,
		] { #2 }
	}
}

\NewDocumentCommand { \MakeBooklet } { O{0mm} m } {
	\int_zero:N \l_impose_counter_int
	\dim_zero:N \l_impose_creep_dim
	\pdfximage { #2 .pdf }
	\int_set:Nn \l_impose_total_pages_int
	{ \the \pdflastximagepages }
	\int_compare:nTF { \int_mod:nn { \l_impose_total_pages_int } { 4 } != 0 } {
		\int_set:Nn \l_impose_total_pages_to_four_int
		{ \l_impose_total_pages_int + 4 - \int_mod:nn { \l_impose_total_pages_int } { 4 } }
	} {
		\int_set_eq:NN \l_impose_total_pages_to_four_int \l_impose_total_pages_int
	}
	\int_set:Nn \l_impose_repetitions_int
	{ \l_impose_total_pages_to_four_int / 2 }
	\int_do_while:nn { \l_impose_counter_int < \l_impose_repetitions_int } {
		\clearpage
		\int_incr:N \l_impose_counter_int
		\begin{tikzpicture}[remember~picture, overlay]
			\node at ($
			(current~page.north)
			-
			(\dim_use:N \l_impose_creep_dim, 0)
			$) {
				\impose_get_page:nn
				{ \int_use:N \l_impose_counter_int }
				{ #2 }
			};
			\node at ($
			(current~page.north~west)
			+
			(\dim_use:N \l_impose_creep_dim, 0)
			$) {
				\impose_get_page:nn
				{ \int_eval:n { \l_impose_total_pages_to_four_int - \l_impose_counter_int + 1 } }
				{ #2 }
			};
		\end{tikzpicture}
		\clearpage
		\int_incr:N \l_impose_counter_int
		\begin{tikzpicture}[remember~picture, overlay]
			\node at ($
			(current~page.north~west)
			+
			(\dim_use:N \l_impose_creep_dim, 0)
			$) {
				\impose_get_page:nn
				{ \int_use:N \l_impose_counter_int }
				{ #2 }
			};
			\node at ($
			(current~page.north)
			-
			(\dim_use:N \l_impose_creep_dim, 0)
			$) {
				\impose_get_page:nn
				{ \int_eval:n { \l_impose_total_pages_to_four_int - \l_impose_counter_int + 1 } }
				{ #2 }
			};
		\end{tikzpicture}
		\dim_set:Nn \l_impose_creep_dim {
			#1 * \l_impose_counter_int / 2
		}
	}
}

\ExplSyntaxOff


\begin{document}
	
	% #1 = Verschiebung pro Bogen (optional)
	% #2 = Dateiname (ohne Endung!). Datei muss eine PDF sein!
	\MakeBooklet[0.24mm]{calender}
	
\end{document}