I use a Macbook, > so the PDF X-Change Viewer won't work for me as it is Windows based.
You already have the software to annotate PDFs on your machine: http://www.apple.com/pro/tips/pdf_annotation.html. It doesn’t have all the features of X-Change viewer but it should be sufficient. See here for guidelines http://www.ehow.com/how_4493222_add-notes-annotate-pdf-os.html. Unfortunately, we don’t have a Mac to test things on.