How to vertically cut a PDF into half i.e 2 pieces - 2 pages or 2 separate files

[javadevelopment4]

We can able to convert A4 PDF to Booklet PDF via PrintDF ([https://github.com/Raudius/PrintDF/blob/master/src/us/raudi/printdf/PrintDF.java)]

However not able to convert Booklet to A4 i.e that is cutting vertically of a Booklet PDF page and resequence all the pages.

1st problem is not sure how to cut veritically each and every PDF page and save as 2 separate PDF page or file

2nd re-sequence of the booklet to proper sequence as 1, 2, 3, 4, 5 by first identifying the actual book sequence (http://www.boooks.org/index.php?page=21&lng=1)

Can you please attach an example or source code to convert booklet to A4 PDF?