Fonts in iBooks
I have recently downloaded the opendyslexic font on my iPad but it won’t appear on the font list in iBooks. How can I use this font to read books?
Can you use the font in an app like Pages? If so, and it won't appear in iBooks, I don't think it is possible, each app is different regarding the use of downloaded fonts. You might be able to use it in a different ereader app, but books bought from Apple's store can normally only be read in iBooks.