Question : I need to identify and count unique words in a group of documents

I have a group of documents that I am trying to assess the most frequently used words in.
I am looking for a tool (similar to a wordpress tag cloud) that will run through a series of docs (Office and PDF) to create a list of the words used and their frequency across all docs.
I am happy to do it one at a time as the group is not overly large, but do need to be able to do both word and pdf files.

Answer : I need to identify and count unique words in a group of documents

it is kind of manual but this works.... http://tagcrowd.com/