I try to select an area of my pdf to make a link, but the selected box seems to only be allowed to be certain sizes. It's selecting two whole lines of text. I can't resize the link area very precisely using the "handles" on the corners of the link area, as directed by the help file.
Answering myself: Change the grid size in Acrobat: Edit / Preferences / Units & Guides / and reduce the size of the "Width between lines" and "Height between lines" values. Then selections can be more precise, the grid is now smaller.