Click Tools on the toolbar -> hit Freehand and you can draw on the pages freely.
Click the freehand drawing, press Delete on the keyboard, or right click -> Delete.
Change the Properties of Freehand
You can change the properties of freehand by doing one of the followings:
1. Click the freehand drawing, then you can change its color and opacity in the annotation properties panel on the right side;
2. Click the freehand drawing and drag the selection handle to resize the signature;
3. Click and drag the freehand drawing to any area as you wish.
Note: if the annotation properties panel is hidden, click the triangle icon on the right side to show it.