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// For complete examples and data files, please go to https://github.com/groupdocs-watermark/GroupDocs.Watermark-for-.NET
using (Document doc = Document.Load(Utilities.MapSourceFilePath (DocFilePath)))
{
    Font font = new Font("Calibri", 8);
    TextWatermark watermark = new TextWatermark("Test watermark", font);
    watermark.HorizontalAlignment = HorizontalAlignment.Right;
    watermark.VerticalAlignment = VerticalAlignment.Top;
    watermark.SizingType = SizingType.ScaleToParentDimensions;
    watermark.ScaleFactor = 0.5;

    // Set rotation angle
    watermark.RotateAngle = 45;

    doc.AddWatermark(watermark);
    doc.Save();
}