Originally Posted by DaleDe
Interesting. Generally changing the font size is an eBook Reader feature and independent of the book. But some eBook Readers will not use this feature to override the CSS in the book itself. I suspect the eBook you checked out has an explicit size set in the book which is why you are having the problem. Even with Library DRM you may be able to open the ePub using 7zip and take a look at the CSS. You might even be able to change it. DRM is generally applied to the html files and embedded font files inside the ePub but not the other ones. I suspect other eBooks you check out will not have this problem. What kind of reader are you using? You might want to report this problem to the library.
I would guess melaine57's findings are typical. I think I see similar behavior. If I buy an ADE EPub, there is probably a 50/50 chance I would have problems using formatting options. I see this on my Kobo (trying to change font, line spacing, margins), and I think I saw the same thing on my Nook Touch (font name). I'm guessing that by buying the store branded epub (kepub, B&N DRM'd epub), the stores are tailoring the epub to ensure it behaves nicely with their readers?