Try another PDF reader.
I deleted the first page and made the document searchable and optimized it using PDF Converter Professional. I viewed quite a few pages (not all) on my Pocket eDGe (another Android tablet) using ezPDF Reader (http://download.pandaapp.com/android....2-id6423.html
) and I didn't see any missing letters. Even the smallest equations were intact. If you tell me what page(s) the missing letters are on I'll see if I can view them using ezPDF. Or you can downloaded ezPDF using the link above or you can buy the Pro version from Amazon (http://www.amazon.com/Unidocs-Inc-ez...keywords=ezpdf
), and download the optimized PDF from my Dropbox and see if it helps: