How do I change font size on pdf

I scanned a generc Monthly Rental Agreement to pdf and entered text fields to be completed as needed for my rental properties.  One section allows for additional terms and comments.  I can't seem to be able to create on large text field that allows me to type in a number of additional items; I can only enter multiple text fields for each item but them the font is larger or smaller depending on the amount of information in that line.  I would like to have one large text field that allows me to enumerate additional items but creating a large text field creates large fonts to match....is there a solution?? thanxzz