Protect and Unprotect worksheets

VSTO
Spire.XLS
Download Sample Code

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Xml.Linq;
using Excel = Microsoft.Office.Interop.Excel;
using Office = Microsoft.Office.Core;
using Microsoft.Office.Tools.Excel;
using System.Reflection;

namespace VSTO
{
    public partial class ThisAddIn
    {
        private void ThisAddIn_Startup(object sender, System.EventArgs e)
        {
            //Add a new workbook
            Excel.Workbook excelApp = this.Application.Workbooks.Add();

            //Protect the worksheet with password
            ((Excel.Worksheet)excelApp.ActiveSheet).Protect("Spire");  

            //Unprotect the worksheet specifying its password
            ((Excel.Worksheet)excelApp.ActiveSheet).Unprotect("Spire");   
        
            //Save the file
            excelApp.SaveAs("Result.xlsx");                       
          
        }

        private void ThisAddIn_Shutdown(object sender, System.EventArgs e)
        {
        }

        #region VSTO generated code

        /// <summary>
        /// Required method for Designer support - do not modify
        /// the contents of this method with the code editor.
        /// </summary>
        private void InternalStartup()
        {
            this.Startup += new System.EventHandler(ThisAddIn_Startup);
            this.Shutdown += new System.EventHandler(ThisAddIn_Shutdown);
        }
        
        #endregion
    }
}

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading.Tasks;
using Spire.Xls;

namespace Spire.XLS
{
    class Program
    {
        static void Main(string[] args)
        {
            //Initialize a new instance of workbook
            Workbook wb = new Workbook();

            //Protect the worksheet with password
            Worksheet sheet = wb.Worksheets[0];
            sheet.Protect("Spire", SheetProtectionType.None);

            //Unprotect the worksheet specifying its password
            sheet.Unprotect("Spire");

            //Save and Launch
            wb.SaveToFile("Result.xlsx");
            System.Diagnostics.Process.Start("Result.xlsx");


        }
    }
}

ProtectAndUnprotect.zip