MergePDF is a free iOS application with which you can easily merge and combine multiple pdf files to a single one. MergePDF is very simple to use. You can use this application to merge PDF files right on your iPhone, iPod touch or iPad. In addition, MergePDF provides Dropbox support to access your files easily across all your devices.
Requires iOS 5.0 or later. Compatible with iPhone, iPad, and iPod touch.