We're having the same problems with the sharpness of the resulting image, and I think I also found the cause.
I also noticed the PdfViewer.PrintDocumentWithSettings places the image on a fixed position and we needed to do some extra stuff too, so instead we used the System.Drawing.Printing.PrintDocument and PdfViewer.DecodePage construction instead.
What's happening is that the image always seems to be returned in the same size. No matter what resolution I set. My A3 document always is returned as a 17Mb Bitmap. No matter what I do with the resolution. I would expect a lower resolution would reduce the bitmap size.
Now when you try to print this with DrawImage(bitmap. e.MarginBounds), the bitmap is scaled and this is the cause of the blurry image, since bitmaps don't scale as well as vector images.
I also tried the PdfConverter.GetNextImage with the resolution X en Y overload but, even though the resulting image is smaller, the quality is exactly the same. I suspect the GetNextImage also does postprocessing on the image instead of doing something with the process that creates those images.
So the cause of this blurry image seems to be the resizing of the BitMap image instead of the Vectors in the PDF decoding.
I hope this helps.