A couple of years ago, someone posted (https://tex.stackexchange.com/a/53366/2966) claiming
After scanning a book 2-up, you can use
pdfpagesandifthento split the pages in two and reassemble 1-up.
I have a PDF document “printed” 2-up, so that on each ANSI-A (8½″×11″) page there are two 5½″×8½″ pages I’d like to extract. How do I go about this?
I can do this manually by writing
\documentclass{minimal}
\usepackage[
papersize={5.5in,8.5in},
margin=0pt, ignoreall,
]{geometry}
\setlength{\parindent}{0pt}
\usepackage{pdfpages,graphicx}
\begin{document}
\includegraphics[viewport= 0 0 396 612, page=1]{two-up.pdf}
\includegraphics[viewport= 396 0 792 612, page=1]{two-up.pdf}
\includegraphics[viewport= 0 0 396 612, page=2]{two-up.pdf}
\includegraphics[viewport= 396 0 792 612, page=2]{two-up.pdf}
% etc.
\end{document}
but this is repetitive and error-prone. Is there a way to do this automatically for the entire book?