To rotate a page in a PDF document.

async function main() {
  const doc = await PDFNet.PDFDoc.createFromURL(filename);

  // Rotate the first page 90 degrees clockwise.
  const page = await doc.getPage(1);
  const originalRotation = await page.getRotation();
  var rotation;
  switch (originalRotation)
  {
    case Page.e_0:   rotation = Page.e_90;  break;
    case Page.e_90:  rotation = Page.e_180; break;
    case Page.e_180: rotation = Page.e_270; break;
    case Page.e_270: rotation = Page.e_0;   break;
    default:         rotation = Page.e_0;   break;
  }
  page.setRotation(rotation);
}
PDFNet.runWithCleanup(main);

A page can be rotated clockwise, by 90 degrees, when displayed or printed. The Page.GetRotation() method returns the Page.Rotate enum specifying the current rotation. Similarly, Page.SetRotation() sets the current rotation.