I have two very simple .pdf files, both generated from Word 2013.
Source.pdf:
This is a line of text at the top of the document.
This is another line just below that.
date: 12/01/14
Target.pdf:
This is a line of text at the top of the document.
This is another line just below that, but with additional text.
date: 12/15/2014
A comparison of these two files returns no changes. Is this something that you can easily reproduce or should I submit some code/files?