I ran into this problem a couple years and found a software program to help with converting PDFs into high-quality PNG files. It's called "ImageMagick" - you'll also want the recommended GhostScript - http://imagemagick.sourceforge.net/http/www/windows.html
It's great for converting individual PDFs or in-bulk via command-line. I would experiment with some of the values in the following discussion - http://stackoverflow.com/questions/6605006/convert-pdf-to-image-with-high-resolution
- Density - I tested various density values (some were too blurry/some were worse than a simple PDF to JPEG conversion) - but found good success at 600 - this does create larger files. I had tried 300 per the stackoverflow link - but I think had problems with that value.
- Rotate by - 90 degrees
- Trim excess space
- Flatten - remove transparency layers (I noticed without this some of my imports into Airwave would show up completely black)
Individual Conversion:
convert -density 600 -rotate -90 -trim -flatten <source-pdf>.pdf <dest-image>.png
Bulk Conversion
mogrify -density 600 -rotate -90 -trim -flatten -format png *.pdf