You hit the nail on the head, Delphin. I seem to have made my error whilst trying to use Calibre. When I avoid that and just dump it on the unit, all's well.
So it's the embedded fonts, which allow me to see the PDF, that also prevent me from converting it to an ePub? Oh the irony!

Would you know any other software I could use to convert it to an ePub or is there no hope? It's not really necessary but it would make reading easier.
Thanks for all your help, Delphin!!!
Take care,
Jashn