I got the solution:
Dim ImgLogoURL As String = Server.MapPath("../Images/Site/logo2.gif")
Dim ImgLogo As iTextSharp.text.Image = iTextSharp.text.Image.GetInstance(ImgLogoURL)
ImgLogo.Annotation = New Annotation(0, 0, 0, 0, "../../default.aspx", 3)
ImgLogo.ScalePercent(50)