Split PDF pages from 2 per sheet to 1 per sheet


#1

I have a PDF file in which every sheet contains 2 pages (side by side in landscape format, so that the PDF’s p. 1 is really the document’s pp. 1 and 2, side by side). How can I convert it to 1 page per sheet, portrait format? (Have basic software, incl Apple Preview, Chrome, etc.)
Thanks!