// 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)))
{
// Initialize image or text watermark
TextWatermark watermark = new TextWatermark("Protected image", new Font("Arial", 8));
watermark.HorizontalAlignment = HorizontalAlignment.Center;
watermark.VerticalAlignment = VerticalAlignment.Center;
watermark.RotateAngle = 45;
watermark.SizingType = SizingType.ScaleToParentDimensions;
watermark.ScaleFactor = 1;
foreach (CellsWorksheet worksheet in doc.Worksheets)
{
if (worksheet.BackgroundImage != null)
{
// Add watermark to the image
worksheet.BackgroundImage.AddWatermark(watermark);
}
}
doc.Save();
}