The sample demonstrates how to Lock Worksheet in Silverlight via Spire.XLS.

<Application xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
             xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml" 
             x:Class="Locksheet_xls.App">
             
    <Application.Resources>
        
    </Application.Resources>
</Application>

using System;
using System.Windows;

namespace Locksheet_xls
{
    public partial class App : Application
    {

        public App()
        {
            this.Startup += this.Application_Startup;
            this.Exit += this.Application_Exit;
            this.UnhandledException += this.Application_UnhandledException;

            InitializeComponent();
        }

        private void Application_Startup(object sender, StartupEventArgs e)
        {
            this.RootVisual = new MainPage();
        }

        private void Application_Exit(object sender, EventArgs e)
        {

        }

        private void Application_UnhandledException(object sender, ApplicationUnhandledExceptionEventArgs e)
        {
            // If the app is running outside of the debugger then report the exception using
            // the browser's exception mechanism. On IE this will display it a yellow alert 
            // icon in the status bar and Firefox will display a script error.
            if (!System.Diagnostics.Debugger.IsAttached)
            {

                // NOTE: This will allow the application to continue running after an exception has been thrown
                // but not handled. 
                // For production applications this error handling should be replaced with something that will 
                // report the error to the website and stop the application.
                e.Handled = true;
                Deployment.Current.Dispatcher.BeginInvoke(delegate { ReportErrorToDOM(e); });
            }
        }

        private void ReportErrorToDOM(ApplicationUnhandledExceptionEventArgs e)
        {
            try
            {
                string errorMsg = e.ExceptionObject.Message + e.ExceptionObject.StackTrace;
                errorMsg = errorMsg.Replace('"', '\'').Replace("\r\n", @"\n");

                System.Windows.Browser.HtmlPage.Window.Eval("throw new Error(\"Unhandled Error in Silverlight Application " + errorMsg + "\");");
            }
            catch (Exception)
            {
            }
        }
    }
}

Imports System.Windows

Namespace Locksheet_xls
	Partial Public Class App
		Inherits Application

		Public Sub New()
			AddHandler Me.Startup, AddressOf Application_Startup
			AddHandler Me.Exit, AddressOf Application_Exit
			AddHandler Me.UnhandledException, AddressOf Application_UnhandledException

			InitializeComponent()
		End Sub

		Private Sub Application_Startup(ByVal sender As Object, ByVal e As StartupEventArgs)
			Me.RootVisual = New MainPage()
		End Sub

		Private Sub Application_Exit(ByVal sender As Object, ByVal e As EventArgs)

		End Sub

		Private Sub Application_UnhandledException(ByVal sender As Object, ByVal e As ApplicationUnhandledExceptionEventArgs)
			' If the app is running outside of the debugger then report the exception using
			' the browser's exception mechanism. On IE this will display it a yellow alert 
			' icon in the status bar and Firefox will display a script error.
			If Not Debugger.IsAttached Then

				' NOTE: This will allow the application to continue running after an exception has been thrown
				' but not handled. 
				' For production applications this error handling should be replaced with something that will 
				' report the error to the website and stop the application.
				e.Handled = True
				Deployment.Current.Dispatcher.BeginInvoke(Sub() ReportErrorToDOM(e))
			End If
		End Sub

		Private Sub ReportErrorToDOM(ByVal e As ApplicationUnhandledExceptionEventArgs)
			Try
				Dim errorMsg As String = e.ExceptionObject.Message + e.ExceptionObject.StackTrace
				errorMsg = errorMsg.Replace(""""c, "'"c).Replace(vbCrLf, vbLf)

				System.Windows.Browser.HtmlPage.Window.Eval("throw new Error(""Unhandled Error in Silverlight Application " & errorMsg & """);")
			Catch e1 As Exception
			End Try
		End Sub
	End Class
End Namespace

<UserControl x:Class="Locksheet_xls.MainPage"
    xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
    xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
    xmlns:d="http://schemas.microsoft.com/expression/blend/2008"
    xmlns:mc="http://schemas.openxmlformats.org/markup-compatibility/2006"
    mc:Ignorable="d"
    d:DesignHeight="300" d:DesignWidth="400">

    <Grid x:Name="LayoutRoot" Background="White" Loaded="LayoutRoot_Loaded">
        <Button Content="RUN" Height="23" HorizontalAlignment="Left" Margin="313,265,0,0" Name="button1" VerticalAlignment="Top" Width="75" Click="button1_Click" />
    </Grid>
</UserControl>    

using System.Windows;
using System.Windows.Controls;
using System.IO;
using System.Reflection;

using Spire.Xls;

namespace Locksheet_xls
{
    public partial class MainPage : UserControl
    {
        private Workbook workbook = null;
        private SaveFileDialog saveFileDialog = null;
        public MainPage()
        {
            InitializeComponent();
            this.workbook = new Workbook();
            this.saveFileDialog = new SaveFileDialog();
            this.saveFileDialog.Filter = "Excel Document(*.xlsx)|*.xlsx";
        }

        private void button1_Click(object sender, RoutedEventArgs e)
        {
            //get the first worksheet and name it
            Worksheet sheet = workbook.Worksheets[0];
            sheet.Name = "protectedSheet";

            //lock the first worksheet of workbook
            sheet.Protect("test");

            //save the workbook
            bool? result = this.saveFileDialog.ShowDialog();
            if (result.HasValue && result.Value)
            {
                using (Stream stream = this.saveFileDialog.OpenFile())
                {
                    this.workbook.SaveToStream(stream);
                }
            }
           
        }

        private void LayoutRoot_Loaded(object sender, RoutedEventArgs e)
        {
            //load the excel template
            Assembly assembly = this.GetType().Assembly;
            foreach (string name in assembly.GetManifestResourceNames())
            {
                if (name.EndsWith("data.xlsx"))
                {
                    using (Stream stream = assembly.GetManifestResourceStream(name))
                    {
                        this.workbook.LoadFromStream(stream, ExcelVersion.Version2010);
                    }
                }
            }
        }
    }
}

Imports System.Windows
Imports System.Windows.Controls
Imports System.IO
Imports System.Reflection

Imports Spire.Xls

Namespace Locksheet_xls
	Partial Public Class MainPage
		Inherits UserControl
		Private workbook As Workbook = Nothing
		Private saveFileDialog As SaveFileDialog = Nothing
		Public Sub New()
			InitializeComponent()
			Me.workbook = New Workbook()
			Me.saveFileDialog = New SaveFileDialog()
			Me.saveFileDialog.Filter = "Excel Document(*.xlsx)|*.xlsx"
		End Sub

		Private Sub button1_Click(ByVal sender As Object, ByVal e As RoutedEventArgs)
			'get the first worksheet and name it
			Dim sheet As Worksheet = workbook.Worksheets(0)
			sheet.Name = "protectedSheet"

			'lock the first worksheet of workbook
			sheet.Protect("test")

			'save the workbook
			Dim result? As Boolean = Me.saveFileDialog.ShowDialog()
			If result.HasValue AndAlso result.Value Then
				Using stream As Stream = Me.saveFileDialog.OpenFile()
					Me.workbook.SaveToStream(stream)
				End Using
			End If

		End Sub

		Private Sub LayoutRoot_Loaded(ByVal sender As Object, ByVal e As RoutedEventArgs)
			'load the excel template
			Dim [assembly] As System.Reflection.Assembly = Me.GetType().Assembly
			For Each name As String In [assembly].GetManifestResourceNames()
				If name.EndsWith("data.xlsx") Then
					Using stream As Stream = [assembly].GetManifestResourceStream(name)
						Me.workbook.LoadFromStream(stream, ExcelVersion.Version2010)
					End Using
				End If
			Next name
		End Sub
	End Class
End Namespace