To rotate a page in a PDF document.

doc := NewPDFDoc(filename)

// Rotate the first page 90 degrees clockwise.
page := doc.GetPage(1)
originalRotation := page.GetRotation()
var rotation int
if originalRotation == PageE_0 {
  rotation = PageE_90
}
else if originalRotation == PageE_90 {
  rotation = PageE_180
}
else if originalRotation == PageE_180 {
  rotation = PageE_270
}
else if originalRotation == PageE_270 {
  rotation = PageE_0
}
else {
  rotation = Page::E_0
}
page.SetRotation(rotation)

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.