I've just finished creating a PDF of an old government publication, using Affinitiy Publisher. I designed it with a page size of 4.25" x 5.5" -- one quarter the size of a standard sheet of U.S. letter paper. My plan was to print it out quarto on regular grain-long printing paper in portrait mode. Folding it in half on the short axis first, then again, would result in a fairly small book (which is fine for this project) with the grain parallel to the spine.

The problem is that now I've got this PDF and discover the imposition software I've used so far (Booklet Creator) only does folio. It can't do quarto imposition. Can anyone point me towards software that can handle this?