Is it possible to reorder an already generated PDF file programmatically, and using as little resources as possible, as this will need to be ran on ~8000 PDFs every month or so?
We are currently using iTextSharp to merge the PDF’s in to larger PDF’s, but iTextsharp’s Documentation does not really explain much.
The Merger product from DynamicPDF will do this (http://www.dynamicpdf.com/). I cannot speak to what kind of performance you'll see with 8k documents, but i can say that it is one of the fastest PDF processing tools i have found.
There is a .Net version of both the Merger tool, and the Generator tool.
I've used iTextSharp -- check out this code sample, it's what I used to write a (simpler) splitting utility.
I've used this on over 10,000 PDFs in a shot, and I can't remember the exact performance, but it was certainly acceptable for a batch job.