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A square annotation displays a rectangle or square 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 square or a rectangle.

Use the SquareAnnotation class to add square annotations to a PDF document.
async function squareAnnotation() {
pushObjectManager();
const doc = new PdfDocument();
const page = doc.newPage();
let rc = { x: 50, y: 50, width: 250, height: 40 };
const layout = new Layout({
runs: [{
text: "A square annotation drawn with a 3pt wide orange line around this note has a rich text " +
"associated with it.",
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, 10, 10)
//Create an instance of SquareAnnotation class and set its relevant properties
const squareAnnot = new SquareAnnotation();
squareAnnot.userName = "Jaime Smith";
squareAnnot.rect = rc;
squareAnnot.lineWidth = 3;
squareAnnot.color = "Orange";
squareAnnot.richText = "<body><p>This <b><i>rich text</i></b> is associated with the square annotation around a text note.</p></body>";
page.annotations.add(squareAnnot); //Add the square annotation
const docData = doc.savePdf();
Util.saveFile("SquareAnnotation.pdf", docData);