' For complete examples and data files, please go to https://github.com/groupdocs-watermark/GroupDocs.Watermark-for-.NET
Using doc As CellsDocument = Document.Load(Of CellsDocument)(Utilities.MapSourceFilePath(FilePath))
' Initialize image or text watermark
Dim watermark As 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
For Each worksheet As CellsWorksheet In doc.Worksheets
If worksheet.BackgroundImage IsNot Nothing Then
' Add watermark to the image
worksheet.BackgroundImage.AddWatermark(watermark)
End If
Next
doc.Save()
End Using