What you describe is exactly what both my method and "Book fold" (if your
version has that feature) do. You print two A5 pages on a single A4 sheet,
to be folded into an A5 booklet. And note that neither method prints 1 and 2
on one sheet, 3 and 4 on the next, etc. Both methods print pages 12 and 1, 2
and 11, 10 and 3, and so on.
If your pages have been created as A4 rather than A5, then you'll need to
take your chances with Word's "2 pages per sheet" option in the Print
dialog, entering the page numbers in the appropriate order.
