Split A4 PDF page into two A5 and back again

Answer 1

Try iText library http://itextpdf.com/. You can use existing pdf file for pattern, edit rotate and split existing documents. Usefull samples you can find here: http://www.1t3xt.info/examples/browse/

Answer 2

I once did something like that with camlpdf. In my case, I had a PDF where a physical A4 page consisted of two logical A5 pages and I wanted to get a normal PDF with A5 pages (i.e. where logical and physical page were the same).

This was in OCaml (camlpdf also exists for F#) and my code was the following:

let pdf = Pdfread.pdf_of_file None in_file ;;

let pdf =
  let (pdf,_perms) = Pdfcrypt.decrypt_pdf "" pdf in
  match pdf with
  | Some pdf -> pdf
  | None -> failwith "Could not decrypt"
;;

let pdf = Pdfmarks.remove_bookmarks pdf ;;

let pages = Pdfdoc.pages_of_pagetree pdf ;;

let pages = List.fold_right (fun page acc ->
  let (y1,x1,y2,x2) = Pdf.parse_rectangle page.Pdfdoc.mediabox in
  let box y1 x1 y2 x2 = Pdf.Array
    [ Pdf.Real y1; Pdf.Real x1; Pdf.Real y2; Pdf.Real x2 ]
  in
  let xm = x1 *. 0.5 +. x2 *. 0.5 in
  let pagel = {page with Pdfdoc.mediabox = box y1 x1 y2 xm}
  and pager = {page with Pdfdoc.mediabox = box y1 xm y2 x2}
  in pagel::pager::acc
) pages [] ;;

let pdf = Pdfdoc.change_pages false pdf pages ;;

Pdf.remove_unreferenced pdf ;;

Pdfwrite.pdf_to_file pdf out_file ;;

If iText offers similar abstractions, perhaps you can do something like this. The procedure is the following:

1. Read and (optionally) decrypt the pdf
2. Remove bookmarks (optional)
3. Obtain the pages from the page tree
4. Manipulate the pages: you can rearrange, duplicate and remove pages, and you can change their mediabox (bounding box); that should be enough for your purpose?
5. Reconstruct the document with the new pages
6. Remove unreferenced objects (like a garbage collect)
7. Write out the resulting PDF