PM> Install-Package Spire.Doc

using Spire.Doc;
using Spire.Doc.Documents;
using Spire.Doc.Fields;

namespace MultiLineTextWatermark
{
    class Program
    {
        static void Main(string[] args)
        {
            //加载Word文档
            Document doc = new Document();
            doc.LoadFromFile("Sample.docx");

            //创建形状，并设置大小、文本内容、位置及样式
            ShapeObject shape = new ShapeObject(doc, ShapeType.TextPlainText);
            shape.Width = 60;
            shape.Height =15;
            shape.VerticalPosition = 25;
            shape.HorizontalPosition = 20;
            shape.Rotation = 320;
            shape.WordArt.Text = "内部使用";
            shape.WordArt.FontFamily = "宋体";
            shape.FillColor = System.Drawing.Color.Red;
            shape.StrokeColor = System.Drawing.Color.Red;

            //遍历所有section
            for (int n = 0; n < doc.Sections.Count; n++)
            {
                Section section = doc.Sections[n];

                //获取页眉
                HeaderFooter header = section.HeadersFooters.Header;
                
                //添加段落到页眉
                Paragraph paragraph1 = header.AddParagraph();

                for (int i = 0; i < 5; i++)
                {
                    
                    for (int j = 0; j < 6; j++)
                    {
                        //复制形状并设置多行多列位置
                        shape = (ShapeObject)shape.Clone();
                        shape.VerticalPosition = 50 + 150 * i;
                        shape.HorizontalPosition = 20 + 160 * j;
                        
                        //添加形状到段落
                        paragraph1.ChildObjects.Add(shape);
                    }
                }
            }

            //保存文档
            doc.SaveToFile("result.docx", FileFormat.Docx2013);
        }
    }
}

Imports Spire.Doc
Imports Spire.Doc.Documents
Imports Spire.Doc.Fields

Namespace MultiLineTextWatermark
	Class Program
		Private Shared Sub Main(args As String())
			'加载Word文档
			Dim doc As New Document()
			doc.LoadFromFile("Sample.docx")

			'创建形状，并设置大小、文本内容、位置及样式
			Dim shape As New ShapeObject(doc, ShapeType.TextPlainText)
			shape.Width = 60
			shape.Height = 15
			shape.VerticalPosition = 25
			shape.HorizontalPosition = 20
			shape.Rotation = 320
			shape.WordArt.Text = "内部使用"
			shape.WordArt.FontFamily = "宋体"
			shape.FillColor = System.Drawing.Color.Red
			shape.StrokeColor = System.Drawing.Color.Red

			'遍历所有section
			For n As Integer = 0 To doc.Sections.Count - 1
				Dim section As Section = doc.Sections(n)

				'获取页眉
				Dim header As HeaderFooter = section.HeadersFooters.Header

				'添加段落到页眉
				Dim paragraph1 As Paragraph = header.AddParagraph()

				For i As Integer = 0 To 4

					For j As Integer = 0 To 5
						'复制形状并设置多行多列位置
						shape = DirectCast(shape.Clone(), ShapeObject)
						shape.VerticalPosition = 50 + 150 * i
						shape.HorizontalPosition = 20 + 160 * j

						'添加形状到段落
						paragraph1.ChildObjects.Add(shape)
					Next
				Next
			Next

			'保存文档
			doc.SaveToFile("result.docx", FileFormat.Docx2013)
		End Sub
	End Class
End Namespace