I'm still trying to solve this problem. What I learned today though is troubling. I used photoshop to open the PDF, adjusted the image to black and white and saved it as a tif as a single band. When I bring the TIF into ArcGIS and symbolize it as two classes, all the ArcScan tools edit the image properly. If I take the TIF and export it to another TIF, the new TIF has the same problem as noted in my previous message. This is disturbing because after I georectify the image using ArcGIS and create a new georectified image, it cannot be "cleaned" with all the ArcScan tools. So, what is happening that ArcGIS is rendering a TIF it cannot function properly with???