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A circle annotation displays a circle or ellipse on the page. When opened, the annotation displays a pop-up window containing the associated note.
The shape of the annotation depends on the dimensions of its bounding rectangle, so it can appear as either a circle or an ellipse.

Use the CircleAnnotation class to add circle annotations to a PDF document.
const doc = new PdfDocument();
const page = doc.newPage();
let rc = { x: 50, y: 50, width: 120, height: 50 };
const layout = new Layout({
runs: [{
text: "A circle annotation drawn with a 3pt wide green line",
font: Font.getPdfFont(StandardPdfFont.Times),
fontSize: 11
}],
maxWidth: rc.width,
maxHeight: rc.height
});
page.context.drawLayout(layout, rc.x, rc.y);
rc = Util.inflate(rc, 15, 24)
//Create an instance of CircleAnnotation class and set its relevant properties
const circleAnnot = new CircleAnnotation();
circleAnnot.userName = "Jaime Smith";
circleAnnot.rect = rc;
circleAnnot.lineWidth = 3;
circleAnnot.color = "Green";
circleAnnot.contents = "This is a circle annotation";
page.annotations.add(circleAnnot); //Add the circle annotation
const docData = doc.savePdf();
Util.saveFile("CircleAnnotation.pdf", docData);