Impossible to change the texte size

I bought Artemis Fowl - part 4 - for my son. He really enjoyed the first 3 but this one is impossible to read as you can not change the font size. It’s some kind of basic pdf. All the first 3 were versions that I could customize to make it bigger. My son is sight impaired and my only raison to buy ebooks is because you can customize the text size.

There is no support or refund from Apple, I find this very frustrating.