It seems that if you remove the embedded fonts within a PDF than the system fonts shall be used. Then the PDF viewer will be forced to search for necessary font or a replacer in the local file system (in the PB90x). Now here's the trick: to have a local font that is improved for the reader !
Here is explained
why the windows fonts are not the best for an ebook reader:
https://sites.google.com/a/etccreati.../kdesignworks/
Here is explained
how a windows font can be optimized for an ebook reader:
https://sites.google.com/a/etccreati.../fontrendering
Someone smart enough might be able to extract then remove an embedded font from a PDF, then adapt it for PB90x and install it on PB90x, then could open the altered PDF to see how the rendering is improved
.
That smart guy I'm sure that will be venerated here
.