As you markup your PDFs more and more, it seems that your digital page gets covered. This makes it difficult to read after some time. You can select each text box and manually resize the box to get rid of extra space or you can use the auto-size function to save a little time. Simply select the text box and press "Alt+Z". Better yet, press "Ctrl+A" to select all markup and then press "Alt+Z" to auto-size the text boxes. See below for an example. Also, remember that you can auto-size the font of a text box by checking the "auto" box next to the font size in the properties tab.
Before clean up
After Clean Up