Files to look at:
The PDF Viewer allows you to draw graphics in a PDf file in the Control.Paint event handler. Use the PDF Graphics API to save graphics to a file.
IMPORTANT You need a license for the DevExpress Office File API Subscription or DevExpress Universal Subscription to use PDF Graphics API in production code.
In this example, a rectangle is drawn in the selection area. Drawing is activated on the Activate Drawing button click. The Save Graphics and Reload button saves created graphics and reloads the PDF file.
Refer to the following article for more information:
How to: Draw Graphics by Coordinates Obtained from the PDF Viewer