有时我们需要在Excel工作表中添加水印来达到保护文档的目的。该文将介绍如何使用C# 在Excel表格中添加自定义页眉，再添加图片或艺术字来模拟Excel水印。Excel 水印在正常模式下不可见，仅在页面布局模式或打印预览模式才可见。

效果图：

using Spire.Xls;
using System.Drawing;
using System;

namespace AddWaterMarktoExcel
{
    class Program
    {
        static void Main(string[] args)
        {
            //加载示例文档
            Workbook workbook = new Workbook();
            workbook.LoadFromFile("Sample.xlsx");

            //设置文本和字体大小
            Font font = new System.Drawing.Font("仿宋", 40);
            String watermark = "内部文档";         
 
            foreach (Worksheet sheet in workbook.Worksheets)
            {
                //调用DrawText() 方法插入图片
                System.Drawing.Image imgWtrmrk = DrawText(watermark, font, System.Drawing.Color.LightCoral, System.Drawing.Color.White, sheet.PageSetup.PageHeight, sheet.PageSetup.PageWidth);
                //将图片设置为页眉
                sheet.PageSetup.LeftHeaderImage = imgWtrmrk;
                sheet.PageSetup.LeftHeader = "&G";
                //将显示模式设置为Layout
                sheet.ViewMode = ViewMode.Layout;
            }
            workbook.SaveToFile("result.xlsx", ExcelVersion.Version2010);
            System.Diagnostics.Process.Start("result.xlsx");
        }

        private static System.Drawing.Image DrawText(String text, System.Drawing.Font font, Color textColor, Color backColor, double height, double width)
        {
            //定义图片宽度和告诉
            Image img = new Bitmap((int)width, (int)height);
            Graphics drawing = Graphics.FromImage(img);
            //获取文本size
            SizeF textSize = drawing.MeasureString(text, font);
            //文本显示样式及位置
            drawing.TranslateTransform(((int)width - textSize.Width) / 2, ((int)height - textSize.Height) / 2);
            drawing.RotateTransform(-45);
            drawing.TranslateTransform(-((int)width - textSize.Width) / 2, -((int)height - textSize.Height) / 2);
            drawing.Clear(backColor);
            Brush textBrush = new SolidBrush(textColor);
            drawing.DrawString(text, font, textBrush, ((int)width - textSize.Width) / 2, ((int)height - textSize.Height) / 2);
            drawing.Save();
            return img;
        }
    }
}

Imports Spire.Xls
Imports System.Drawing

Namespace AddWaterMarktoExcel
	Class Program
		Private Shared Sub Main(args As String())
			'加载示例文档
			Dim workbook As New Workbook()
			workbook.LoadFromFile("Sample.xlsx")

			'设置文本和字体大小
			Dim font As Font = New System.Drawing.Font("仿宋", 40)
			Dim watermark As [String] = "内部文档"

			For Each sheet As Worksheet In workbook.Worksheets
				'调用DrawText() 方法插入图片
				Dim imgWtrmrk As System.Drawing.Image = DrawText(watermark, font, System.Drawing.Color.LightCoral, System.Drawing.Color.White, sheet.PageSetup.PageHeight, sheet.PageSetup.PageWidth)
				'将图片设置为页眉
				sheet.PageSetup.LeftHeaderImage = imgWtrmrk
				sheet.PageSetup.LeftHeader = "&G"
				'将显示模式设置为Layout
				sheet.ViewMode = ViewMode.Layout
			Next
			workbook.SaveToFile("result.xlsx", ExcelVersion.Version2010)
			System.Diagnostics.Process.Start("result.xlsx")
		End Sub

		Private Shared Function DrawText(text As [String], font As System.Drawing.Font, textColor As Color, backColor As Color, height As Double, width As Double) As System.Drawing.Image
			'定义图片宽度和告诉
			Dim img As Image = New Bitmap(CInt(width), CInt(height))
			Dim drawing As Graphics = Graphics.FromImage(img)
			'获取文本size
			Dim textSize As SizeF = drawing.MeasureString(text, font)
			'文本显示样式及位置
			drawing.TranslateTransform((CInt(width) - textSize.Width) / 2, (CInt(height) - textSize.Height) / 2)
			drawing.RotateTransform(-45)
			drawing.TranslateTransform(-(CInt(width) - textSize.Width) / 2, -(CInt(height) - textSize.Height) / 2)
			drawing.Clear(backColor)
			Dim textBrush As Brush = New SolidBrush(textColor)
			drawing.DrawString(text, font, textBrush, (CInt(width) - textSize.Width) / 2, (CInt(height) - textSize.Height) / 2)
			drawing.Save()
			Return img
		End Function
	End Class
End Namespace