PageHeight

public double PageHeight { get; set; }

Document doc = new Document();
DocumentBuilder builder = new DocumentBuilder(doc);

// Insérez l'image dans l'en-tête afin qu'elle soit visible sur chaque page.
builder.MoveToHeaderFooter(HeaderFooterType.HeaderPrimary);
Shape shape = builder.InsertImage(ImageDir + "Transparent background logo.png");
shape.WrapType = WrapType.None;
shape.BehindText = true;

// Placez l'image au centre de la page.
shape.RelativeHorizontalPosition = RelativeHorizontalPosition.Page;
shape.RelativeVerticalPosition = RelativeVerticalPosition.Page;
shape.Left = (builder.PageSetup.PageWidth - shape.Width) / 2;
shape.Top = (builder.PageSetup.PageHeight - shape.Height) / 2;

doc.Save(ArtifactsDir + "DocumentBuilder.InsertWatermark.docx");