Do you have any components that can detect changes between versions of a PDF and display the changes using different colors of addictions and subtractions?
For PDF comparison, you could use pdftron.PDF.PDFDraw.GetBitmap() as shown in PDFDraw sample:
Once you have two images you can compare them with any image diff utility (e.g.image magic, opencv, http://pdiff.sourceforge.net etc).
You can add highlights to existing PDF pages using ‘pdftron.PDF.Stamper’ (http://www.pdftron.com/pdfnet/samplecode.html#Stamper) or ElementBuilder/ElementWriter (see ‘How do I add a watermark to a page?’ in http://www.pdftron.com/pdfnet/faq.html). The latter option offers more flexibility at the expense of extra coding.