This article explains how you can zoom in on part of a page by using pinch to zoom.
Pinch to zoom lets you magnify any area of a notebook. Use this feature to focus on the part of the page you’re working on.
How to zoom in and out
Pinch with two fingers to zoom in on the part of the page you want to see. Pinch out to zoom out.
Navigate the page
Once you’ve zoomed in, you can move around the magnified area by using two fingers.
Use the selection tool while zoomed in for making precise changes.