public void TestNPOI()
{
    string sourceFile = @"D:\sourceFile.xlsx";
    string targetFile = @"D:\targetFile.xlsx";
 
    IWorkbook workbook = new XSSFWorkbook(sourceFile);
    ISheet sheet1 = workbook.GetSheet("Sheet1");
 
    sheet1.CreateRow(0).CreateCell(0).SetCellValue(1);
    sheet1.CreateRow(1).CreateCell(0).SetCellValue(2);
    sheet1.CreateRow(2).CreateCell(0).SetCellValue(3);
 
    FileStream fs = new FileStream(targetFile, FileMode.Create);
    workbook.Write(fs);
    workbook.Close();
}

public void TestEPPlus()
{
    string sourceFile = @"D:\sourceFile.xlsx";
    string targetFile = @"D:\targetFile.xlsx";
 
    ExcelPackage.LicenseContext = LicenseContext.NonCommercial;//指明非商业应用
    ExcelPackage package = new ExcelPackage(sourceFile);//加载Excel工作簿
    ExcelWorksheet sheet1 = package.Workbook.Worksheets["Sheet1"];//读取工作簿中名为"Sheet1"的工作表
 
    sheet1.Cells[1, 1].Value = "A";//设置单元格内容
    sheet1.Cells[2, 2].Value = "B";
    sheet1.Cells[3, 3].Value = "C";
 
    sheet1.Cells[1, 2].Value = "1";
    sheet1.Cells[2, 2].Value = "2";
    sheet1.Cells[3, 2].Value = "3";
 
    //package.Save();//将更改保存到原文件
    package.SaveAs(targetFile);//将更改保存到新的文件，类似于另存为
}

public void TestSpireOffice()
{
    string sourceFile = @"D:\sourceFile.xlsx";
    string targetFile = @"D:\targetFile.xlsx";
 
    Workbook workbook = new Workbook();
    workbook.LoadFromFile(sourceFile);//加载Excel工作簿
    Worksheet sheet1 = workbook.Worksheets["Sheet1"];//读取工作簿中名为"Sheet1"的工作表
 
    sheet1.SetCellValue(1, 1, "A");//设置单元格内容
    sheet1.SetCellValue(2, 1, "B");
    sheet1.SetCellValue(3, 1, "C");
 
    sheet1.SetCellValue(1, 2, "1");
    sheet1.SetCellValue(2, 2, "2");
    sheet1.SetCellValue(3, 2, "3");
 
    workbook.Save();//将更改保存到原文件
    workbook.SaveToFile(targetFile);//将更改保存到新的文件，类似于另存为
}