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// For complete examples and data files, please go to https://github.com/groupdocs-watermark/GroupDocs.Watermark-for-.NET
using (CellsDocument doc = Document.Load<CellsDocument>(Utilities.MapSourceFilePath (FilePath)))
{
    TextWatermark watermark = new TextWatermark("Test watermark", new Font("Segoe UI", 19));

    CellsTextEffects effects = new CellsTextEffects();
    effects.LineFormat.Enabled = true;
    effects.LineFormat.Color = Color.Red;
    effects.LineFormat.DashStyle = OfficeDashStyle.DashDotDot;
    effects.LineFormat.LineStyle = OfficeLineStyle.Triple;
    effects.LineFormat.Weight = 1;
    doc.AddTextWatermark(watermark, effects);
    doc.Save();
}