VerticalAnchor

public TextBoxAnchor VerticalAnchor { get; set; }

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

Shape shape = builder.InsertShape(ShapeType.TextBox, 200, 200);

// Set the "VerticalAnchor" property to "TextBoxAnchor.Top" to
// align the text in this text box with the top side of the shape.
// Set the "VerticalAnchor" property to "TextBoxAnchor.Middle" to
// align the text in this text box to the center of the shape.
// Set the "VerticalAnchor" property to "TextBoxAnchor.Bottom" to
// align the text in this text box to the bottom of the shape.
shape.TextBox.VerticalAnchor = verticalAnchor;

builder.MoveTo(shape.FirstParagraph);
builder.Write("Hello world!");

// The vertical aligning of text inside text boxes is available from Microsoft Word 2007 onwards.
doc.CompatibilityOptions.OptimizeFor(MsWordVersion.Word2007);
doc.Save(ArtifactsDir + "Shape.VerticalAnchor.docx");