This article will demonstrate how to add image watermark or text watermark into one or all of the PowerPoint presentation slides using free Spire.Presentation.
Introduction
There are different concepts for what Watermark is, but usually when
we need to add watermark to our documents is either to discourage others from
unauthorized copying or to add a background
to the document to display a confidential or draft status or whatever other
status. Then, how to add a watermark into PowerPoint presentation
programmatically? It can be added in various ways, but one of the best should
probably be Spire.Presentation.
This article will demonstrate how to add image watermark or
text watermark into one or all of the PowerPoint
presentation slides using free Spire.Presentation.
Using the code
Part 1. Add Image Watermark
Create an instance of Presentation
class and load a existing ppt document.
Presentation ppt = new Presentation();
ppt.LoadFromFile(fileName);
Then, get the reference of a slide by using its Index and Set
the Slide Background Type of the Slide to custom, here we have to set it as
custom, otherwise the image won’t be rendered.
ppt.Slides[0].SlideBackground.Type = Spire.Presentation.Drawing.BackgroundType.Custom;
Next, set the FillType of the Slide Background to Picture and
set the FillType of Picture using PictureFillType enum, Here we set the picture
filltype as stretch as below.
ppt.Slides[0].SlideBackground.Fill.FillType = FillFormatType.Picture;
ppt.Slides[0].SlideBackground.Fill.PictureFill.FillType = PictureFillType.Stretch;
Then, instantiate Image object with an image that can be
used for the Slide Background using PictureFill.Picture.EmbedImage.
IImageData image =ppt.Images.Append(Image.FromFile("WaterMark.png"));
ppt.Slides[0].SlideBackground.Fill.PictureFill.Picture.EmbedImage = image;
Last, save it and we will see the effect as below.
ppt.SaveToFile(resultFileName, Spire.Presentation.FileFormat.PPT);

Part 2. Add Text Watermark
In Spire.Presentation the text watermark is based on shape,
and it uses the
locking property of shape to protect the shape from selection and edition. Let’s
take an example.
The first step is same as image watermark creation, which is
to create an instance of Presentation class and load a ppt document. And then
create a shape and apply its formatting, here the important point is that the SelectionProtection property of the
shape must be set to true.
Presentation ppt = new Presentation();
ppt.LoadFromFile(fileName);
RectangleF rect = new RectangleF(82,195,555,149);
IAutoShape shape = ppt.Slides[0].Shapes.AppendShape(Spire.Presentation.ShapeType.Rectangle,
rect);
shape.Fill.FillType = FillFormatType.None;
shape.Line.FillType = FillFormatType.None;
shape.Rotation = -45;
shape.Locking.SelectionProtection = true;
Next, apply formatting to the text with TextFrame property of the shape. Note that there
is no direct property for setting the transparency of the text color, but there
is alpha value
associated with the color that can be used for setting the transparency. Its
value ranges from 0 to 255. 0 means total transparency and 255 means no
transparency.
shape.TextFrame.Text = "Confidential";
shape.TextFrame.TextRange.FontHeight = 90;
shape.TextFrame.TextRange.Fill.FillType = Spire.Presentation.Drawing.FillFormatType.Solid;
shape.TextFrame.TextRange.Fill.SolidColor.Color = Color.FromArgb(70, Color.Black);
At last, save and we see the result as below.
ppt.SaveToFile(resultFileName, Spire.Presentation.FileFormat.PPT);

Conclusion
Spire.Presentation
is a professional PowerPoint® compatible component that enables developers to
create, read, write, modify, convert and Print PowerPoint documents from any
.NET platform. As an independent PowerPoint .NET component, Spire.Presentation
for .NET doesn't need Microsoft PowerPoint installed on the machine.