Typically if you wanted to merge different PDF documents together, you would need to have the Adobe PDF writer software, which costs above US$ 350.

Fortunately now there is a free and convinient way of merging PDF documents and making one PDF document out of it. You can do this online at http://www.mergepdf.net/

There are a few limitiations which are listed below:

- You are limited to combining only 10 pdf files together
- The individual file size of each file should not be more than 10 MegaBytes

The company also claims that all uploaded files are removed once the merge process has finished. I have given this a try and it seemed to work nicely for two PDF documents I tried joining, can't complaint if its free!