Cacher is the code snippet organizer for pro developers

// 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(WatermarkText, new Font("Segoe UI", 19));
    watermark.HorizontalAlignment = HorizontalAlignment.Center;
    watermark.VerticalAlignment = VerticalAlignment.Center;
    watermark.RotateAngle = 45;
    watermark.SizingType = SizingType.ScaleToParentDimensions;
    watermark.ScaleFactor = 0.5;
    watermark.Opacity = 0.5;
    doc.Worksheets[0].AddWatermarkAsBackground(
          watermark,
          doc.Worksheets[0].ContentAreaWidthPx /*set background width*/,
          doc.Worksheets[0].ContentAreaHeightPx /*set background height*/);
    doc.Save();
}