On the toolbar you can manage your annotations.
To add highlight, underline, squiggle, or strikethrough annotations, tap and hold the Text Formatting icon [1].
To type text or add a comment, tap and hold the Free Text icon [2].
To add thin drawing, bold drawing, arrow, line, or shape annotations, tap and hold the Drawing icon [3].
To undo changes, tap the Undo icon [4].
To move the toolbar, tap and hold the drag handle [5], and move it to the new location. The toolbar can be relocated to either side of the screen.