PM> Install-Package Spire.XLS

using Spire.Xls;
using System.Drawing;

namespace 通過頁眉為Excel添加水印
{
    class Program
    {
        static void Main(string[] args)
        {
            // 創(chuàng)建 Workbook 對象
            Workbook workbook = new Workbook();

            // 加載 Excel 文檔
            workbook.LoadFromFile("C:\\Users\\Administrator\\Desktop\\Input.xlsx");

            // 加載圖片文件
            Image image = Image.FromFile("C:\\Users\\Administrator\\Desktop\\confidential.png");

            // 遍歷文件中的所有工作表
            for (int i = 0; i < workbook.Worksheets.Count; i++)
            {
                // 獲取指定工作表
                Worksheet worksheet = workbook.Worksheets[i];

                // 在頁眉中間區(qū)域添加圖片占位符
                worksheet.PageSetup.CenterHeader = "&G";

                // 將圖片添加到頁眉中間位置
                worksheet.PageSetup.CenterHeaderImage = image;
            }

            // 保存結果文件
            workbook.SaveToFile("AddWatermark.xlsx", ExcelVersion.Version2016);

            // 釋放資源
            workbook.Dispose();
        }
    }
}

using Spire.Xls;
using System.Drawing;

namespace 通過背景圖片為Excel添加水印
{
    class Program
    {
        static void Main(string[] args)
        {
            // 創(chuàng)建 Workbook 對象
            Workbook workbook = new Workbook();

            // 加載 Excel 文檔
            workbook.LoadFromFile("C:\\Users\\Administrator\\Desktop\\Input.xlsx");

            // 加載圖片文件
            Bitmap bitmapImage = new Bitmap(Image.FromFile("C:\\Users\\Administrator\\Desktop\\sample.png"));

            // 遍歷文件中的所有工作表
            for (int i = 0; i < workbook.Worksheets.Count; i++)
            {
                // 獲取指定工作表
                Worksheet worksheet = workbook.Worksheets[i];

                // 將圖片設置為工作表背景
                worksheet.PageSetup.BackgoundImage = bitmapImage;
            }

            // 保存結果文件
            workbook.SaveToFile("AddWatermark.xlsx", ExcelVersion.Version2016);

            // 釋放資源
            workbook.Dispose();
        }
    }
}

Install-Package Aspose.Cells

using Aspose.Cells;
using Aspose.Cells.Drawing;
using System.Drawing;

public static void AddTextWatermarkWithAspose()
{
    // 1. 創(chuàng)建工作簿對象（也可直接加載已有文件）
    Workbook workbook = new Workbook();
    
    // 2. 獲取第一個工作表
    Worksheet sheet = workbook.Worksheets[0];
    
    // 3. 添加藝術字形狀作為水印
    // AddTextEffect(預設效果, 水印文字, 字體名, 字號, 字體傾斜, 粗體, 上偏移, 左偏移, 高度, 寬度, 旋轉角度, ZOrder)
    Aspose.Cells.Drawing.Shape watermark = sheet.Shapes.AddTextEffect(
        MsoPresetTextEffect.TextEffect1,
        "機密文檔",
        "Arial Black",
        50,
        false,
        true,
        18, 8, 
        1, 1,
        130, 800
    );
    
    // 4. 設置水印的填充屬性
    watermark.FillFormat.SetOneColorGradient(Color.Red, 0.9, GradientStyleType.Horizontal, 1);
    watermark.FillFormat.Transparency = 0.9;
    
    // 5. 使邊框不可見
    watermark.LineFormat.IsVisible = false;
    
    // 6. 保存工作簿
    workbook.Save("WatermarkedWorkbook.xlsx");
}

using Spire.Xls;
using System.Drawing;

public static void AddWatermarkWithSpire()
{
    Workbook workbook = new Workbook();
    workbook.LoadFromFile("input.xlsx");
    
    // 設置字體
    Font font = new Font("宋體", 40);
    string watermarkText = "內部使用";
    
    foreach (Worksheet sheet in workbook.Worksheets)
    {
        // 根據文本生成圖片水印
        Image img = DrawTextWatermark(watermarkText, font, Color.LightCoral, Color.White, 
                                      sheet.PageSetup.PageHeight, sheet.PageSetup.PageWidth);
        // 將圖片作為頁眉添加到工作表
        sheet.PageSetup.LeftHeaderImage = img;
        sheet.PageSetup.LeftHeader = "&G";
        
        // 切換視圖模式以預覽水印效果
        sheet.ViewMode = ViewMode.Layout;
    }
    
    workbook.SaveToFile("output.xlsx");
}

private static Image DrawTextWatermark(string text, Font font, Color textColor, 
                                         Color backColor, double height, double width)
{
    // 創(chuàng)建一個與工作表頁面大小相同的圖像
    Image img = new Bitmap((int)width, (int)height);
    Graphics drawing = Graphics.FromImage(img);
    
    // 計算文本尺寸并居中
    SizeF textSize = drawing.MeasureString(text, font);
    drawing.TranslateTransform(((int)width - textSize.Width) / 2, 
                                ((int)height - textSize.Height) / 2);
    
    // 設置文字顏色和背景填充
    drawing.DrawString(text, font, new SolidBrush(textColor), 0, 0);
    drawing.FillRectangle(new SolidBrush(backColor), 0, 0, img.Width, img.Height);
    
    // 釋放資源
    drawing.Dispose();
    return img;
}

using OfficeOpenXml;
using System.IO;
public static void AddWatermarkWithEPPlus()
{
    using (ExcelPackage package = new ExcelPackage(new FileInfo("input.xlsx")))
    {
        var worksheet = package.Workbook.Worksheets[0];
        // 在頁眉居中位置插入圖片作為水印
        worksheet.HeaderFooter.OddHeader.InsertPicture(
            new FileInfo("watermark.png"), 
            PictureAlignment.Centered
        );
        worksheet.HeaderFooter.EvenHeader.InsertPicture(
            new FileInfo("watermark.png"), 
            PictureAlignment.Centered
        );
        package.Save();
    }
}