PM> Install-Package Spire.Doc

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

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

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

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

                //加载水印图片
                DocPicture picture = new DocPicture(doc);
                picture.LoadImage("logo.png");
                picture.TextWrappingStyle = TextWrappingStyle.Behind;

                //复制图片
                for (int p = 0; p < 5; p++)
                {
                    for (int q = 0; q < 3; q++)
                    {
                        picture = (DocPicture)picture.Clone();
                        picture.VerticalPosition = 50 + 150 * p;
                        picture.HorizontalPosition = 10 + 140 * q;
                        paragraph1.ChildObjects.Add(picture);
                    }
                }
            }

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

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

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

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

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

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

				'加载水印图片
				Dim picture As New DocPicture(doc)
				picture.LoadImage("logo.png")
				picture.TextWrappingStyle = TextWrappingStyle.Behind

				'复制图片
				For p As Integer = 0 To 4
					For q As Integer = 0 To 2
						picture = DirectCast(picture.Clone(), DocPicture)
						picture.VerticalPosition = 50 + 150 * p
						picture.HorizontalPosition = 10 + 140 * q
						paragraph1.ChildObjects.Add(picture)
					Next
				Next
			Next

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