Handling multiple pdf’s can be a pain, and combining multiple pdf’s is not as easy as merging doc files. So how to achieve this?
The simplest and the fastest way is using pdftk. Install Ubuntu if you are not a regular user, install this on a VirtualBox image and install pdftk on your instance by typing
sudo apt-get install pdftk
Once the installation is complete, you can now start merging pdf files on the fly by using the following command
pdftk *.pdf cat output merged.pdf
or
pdftk 1.pdf 2.pdf 3.pdf cat output merged.pdf
There are mutiple options to this which you can find out using man or using google 
#1 by Zanil Hyder on August 5, 2010 - 8:30 am
are you aware of any windows tools to do the same,without much of a installation hassle.