Lyman,you indicated you exported the PDF image as a reduced-pixel PNG. I downloaded the png, and the Properties indicates it is a 1.1 mb file size, and only 1023 x 812 pixels - not the proper size for out maps and certs.
I am still looking for someone who can scan a color image at 300 dpi, and convert it to a 300 dpi png of the correct dimensions, and have it less than 500 kb.
A scanned PDF likley has background image information that, while we see white, there could be subtle color information contained in the file. That is why it is unlikely that we can scan a color document, convert it to a PDF, and then output a color png of the correct size.
We still need to research this issue, in all of our spare time. That means, I will look at this in January, I believe.