Peled,
Thank you for your reply.
I was kind of expecting the cause that you described since I understand that the PDF format is an open standard created by Adobe but many developers market their own versions of PDF creators including the one I use from Nuance Corp.
So, it appears that the problem is with Paperport scanning/file management software that I use to create the PDF files I tried scanning the document using "gray scale" and "BW" but neither work. Could it be the toner used on those docs because, I can scan and transfer other docs successfully"?