pdfrearrange is a very flexible and powerful program. It allows you to reorder the pages inside existing pdfs. It's simple to use it like a batch application to reorder the pages of every PDF in your archive.
It's simple to use it inside your cgis.
PDFrearrange is a powerful tool for PDF prepress use, the output PDF have the same information like the input file. You can manage big prepress pdf file rearranging pages, removing or duplicating selected pages.

Usage:
pdfrearrange.exe [-options ...]

where options include:
-template "infile.pdf" the template file
-output "outfile.pdf" the output file
-pageorder "order.txt" the new order of pages

You can use the abbreviations "-t", "-o" and "-p".

The license of this software is Free Trial Software, the price is $890.00, you can free download and get a free trial.