PdfTextMarkupAnnotationType API in JavaScript PDF API control

// Load an existing PDF document
let document: PdfDocument = new PdfDocument(data, password);
// Access first page
let page: PdfPage = document.getPage(0);
// Access the annotation at index 0
let annotation: PdfTextMarkupAnnotation = page.annotations.at(0) PdfTextMarkupAnnotation;
// Sets the type of the text markup annotation as underline
annotation.textMarkupType = PdfTextMarkupAnnotationType.underline;
// Save the document
document.save('output.pdf');
// Destroy the document
document.destroy();