newcodeannotation.cs

// Create list of annotations
List<AnnotationBase> annotations = new List<AnnotationBase>()
{
    new AreaAnnotation()
    {
        PageNumber = 0,
        Box = new Rectangle(100, 100, 100, 100),
        Message = "area"
    },
                 
    new EllipseAnnotation()
        {
            PageNumber = 0,
            Box = new Rectangle(200, 200, 80, 80),
            Message = "ellipse"
        }
};
 
// Create annotator
using  (Annotator annotator = new Annotator("input.pdf"))
{
    // Add annotations
    annotator.Add(annotations);
    // Save result to "result.pdf"
    annotator.Save("result.pdf", new SaveOptions());
}