DiagramPageWatermarkOptions

public sealed class DiagramPageWatermarkOptions : DiagramWatermarkOptions

DiagramLoadOptions loadOptions = new DiagramLoadOptions();
using (Watermarker watermarker = new Watermarker(@"D:\test.vsdx", loadOptions))
{
    TextWatermark watermark = new TextWatermark("watermark test", new Font("Arial", 42));

    DiagramPageWatermarkOptions options = new DiagramPageWatermarkOptions();
    options.IsLocked = true;
    options.PageIndex = 0;

    watermarker.Add(watermark, options);
    watermarker.Save();
}