How to merge multiple PDF documents
To merge multiple PDF documents into one you can use pdftk, the free and versatile PDF toolkit from the command-line or from a batch (.BAT) file.
e.g. to merge a.pdf, b.pdf and c.pdf into result.pdf you’d use:
pdftk a.pdf b.pdf c.pdf cat output result.pdf
Also see the PDF Hacks book webpage for a collection of PDF tools.