In iBooks, is it possible to just change the font size for a single book/file, rather then it automatically doing it for all of them?

Basically, I have several files downloaded on my iBooks, and I am wondering is there a way to just adjust the font size for each individual books. I do have a very old iPad(2nd) but I dont think that matters. My books are not all the same font size so once I adjust the font for one of my books it automatically does the same to the other files, which messes with my bookmarks and the font size I liked for those respective books.