font size question

I'm wondering if there is a variable view of fonts for the digital edition.  I need more than the x2 but less than the x3 size.  I am straining my eyes to read my textbook for my course.  Is there any way I can make the font bigger without having to use the mouse to move the screen from side to side?  My kindle can change the font and it rearranges the text to accommodate the size change.  Can the adobe digital editions do this?  Unfortunately, my textbook doesn't come in kindle format.  Can someone advise me, please?

Thanks