Location: In the upper panel there's the annotation toolbar,

 which can be used to highlight, add marks and write notes on the exam:

1. Question mark     2. V mark    3. Half V mark    4. X    5. Marker    6. Arrow    7. line   

 8. Circle    9. Square    10. Scribbling    11. Thickness Selection    12. Color Selection

Using the tool: Click on the desired tool, the selected tool will be active for one use

Click on the exam to add the annotation

Continuous use: Double-clicking with the mouse will allow continuous use of the selected tool. To deselect it,

 click on the tool again or on the "Selection Tool"

Resize and Position: The shapes we've added can be resized, rotated, and dragged across the document

Delete: Select the desired object and press the "trash can" button or the "Delete" key on the keyboard.

 You can delete multiple objects at the same time by marking the area surrounding them