Multi Threaded PDF Merger

I have to merge a ton of PDF's on a daily bases, we using a Commercial Product aka Adobe Acrobat which take almost 1 hour to merge 5000 PDF documents to 5 single one's.

Im Programmer and this wasn't acceptable for me....

This Libary (or Tutorial ?) is the result, its using IText for C# and it's made to use your physical CPU Cores and do Parallel Execution.

I will make it short, 1000 PDF needs 15 seconds(On a 6 Core Machine with 50% Usage Peeks), also the Filesize is 50% smaller than Adobe and there is no visual difference (if there change compression...)!

This save me a lot of time and since this is for my work also money. Adobe may be great for other tasks but not for simple merging.

PS: The GUI Program its just a Demo, its fully functional ofc and im using it, but as the main "point" of this small Project look at the libary and see how i merge them maybe its useful for usage in other Program's.