Added the sample for YouTube video.

Author: deepika134

Videos/Comments/Comments.csproj

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+<Project Sdk="Microsoft.NET.Sdk.Web">
+
+  <PropertyGroup>
+    <TargetFramework>net8.0</TargetFramework>
+    <Nullable>enable</Nullable>
+    <ImplicitUsings>enable</ImplicitUsings>
+  </PropertyGroup>
+
+  <ItemGroup>
+    <PackageReference Include="Syncfusion.XlsIO.Net.Core" Version="31.2.5" />
+  </ItemGroup>
+
+</Project>

Videos/Comments/Controllers/HomeController.cs

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+using System.Diagnostics;
+using Comments.Models;
+using Microsoft.AspNetCore.Mvc;
+using Syncfusion.XlsIO;
+
+namespace Comments.Controllers
+{
+    public class HomeController : Controller
+    {
+        private readonly ILogger<HomeController> _logger;
+
+        public HomeController(ILogger<HomeController> logger)
+        {
+            _logger = logger;
+        }
+
+        public IActionResult AddComment()
+        {
+            // Initialize the Excel engine
+            ExcelEngine excelEngine = new ExcelEngine();
+            IApplication application = excelEngine.Excel;
+            application.DefaultVersion = ExcelVersion.Xlsx;
+
+            // Open the Excel workbook from the specified template
+            IWorkbook workbook = application.Workbooks.Open("Data\\CommentsTemplate.xlsx", ExcelOpenType.Automatic);
+            IWorksheet worksheet = workbook.Worksheets[0];
+
+            // Add a threaded comment to cell H16
+            IThreadedComment threadedComment = worksheet.Range["H16"].AddThreadedComment(
+                "What is the reason for the higher total amount of \"desk\" in the west region?",
+                "User1",
+                DateTime.Now
+            );
+
+            // Export the modified workbook as a downloadable Excel file
+            return ExportWorkbook(workbook, "AddComment.xlsx");
+        }
+
+        public IActionResult ReplyComment()
+        {
+            // Initialize the Excel engine
+            ExcelEngine excelEngine = new ExcelEngine();
+            IApplication application = excelEngine.Excel;
+            application.DefaultVersion = ExcelVersion.Xlsx;
+
+            // Open the workbook containing the comment to reply to
+            IWorkbook workbook = application.Workbooks.Open("Data\\ReplyInput.xlsx", ExcelOpenType.Automatic);
+            IWorksheet worksheet = workbook.Worksheets[0];
+
+            // Access the collection of threaded comments
+            IThreadedComments threadedComments = worksheet.ThreadedComments;
+
+            // Add a reply to the first threaded comment
+            threadedComments[0].AddReply(
+                "The unit cost of desk is higher compared to other items in the west region. As a result, the total amount is elevated.",
+                "User2",
+                DateTime.Now
+            );
+
+            // Export the modified workbook
+            return ExportWorkbook(workbook, "ReplyComment.xlsx");
+        }
+
+        public IActionResult ResolveComment()
+        {
+            // Initialize the Excel engine
+            ExcelEngine excelEngine = new ExcelEngine();
+            IApplication application = excelEngine.Excel;
+            application.DefaultVersion = ExcelVersion.Xlsx;
+
+            // Open the workbook containing the comment to resolve
+            IWorkbook workbook = application.Workbooks.Open("Data\\ResolveInput.xlsx", ExcelOpenType.Automatic);
+            IWorksheet worksheet = workbook.Worksheets[0];
+
+            // Access the threaded comments
+            IThreadedComments threadedComments = worksheet.ThreadedComments;
+
+            // Mark the first comment as resolved
+            threadedComments[0].IsResolved = true;
+
+            // Export the updated workbook
+            return ExportWorkbook(workbook, "ResolveComment.xlsx");
+        }
+
+        public IActionResult DeleteComment()
+        {
+            // Initialize the Excel engine
+            ExcelEngine excelEngine = new ExcelEngine();
+            IApplication application = excelEngine.Excel;
+            application.DefaultVersion = ExcelVersion.Xlsx;
+
+            // Open the workbook containing the comment to delete
+            IWorkbook workbook = application.Workbooks.Open("Data\\DeleteInput.xlsx", ExcelOpenType.Automatic);
+            IWorksheet worksheet = workbook.Worksheets[0];
+
+            // Access the threaded comments
+            IThreadedComments threadedComments = worksheet.ThreadedComments;
+
+            // Delete the first threaded comment
+            threadedComments[0].Delete();
+
+            // Export the updated workbook
+            return ExportWorkbook(workbook, "DeleteComment.xlsx");
+        }
+
+        public IActionResult ClearComment()
+        {
+            // Initialize the Excel engine
+            ExcelEngine excelEngine = new ExcelEngine();
+            IApplication application = excelEngine.Excel;
+            application.DefaultVersion = ExcelVersion.Xlsx;
+
+            // Open the workbook containing comments to clear
+            IWorkbook workbook = application.Workbooks.Open("Data\\ClearInput.xlsx", ExcelOpenType.Automatic);
+            IWorksheet worksheet = workbook.Worksheets[0];
+
+            // Access all threaded comments
+            IThreadedComments threadedComments = worksheet.ThreadedComments;
+
+            // Clear all threaded comments from the worksheet
+            threadedComments.Clear();
+
+            // Export the cleaned workbook
+            return ExportWorkbook(workbook, "ClearComment.xlsx");
+        }
+
+        private FileStreamResult ExportWorkbook(IWorkbook workbook, string fileName)
+        {
+
+            // Create a memory stream to hold the Excel file content
+            MemoryStream stream = new MemoryStream();
+
+            // Save the workbook to the memory stream
+            workbook.SaveAs(stream);
+
+            // Reset the stream position to the beginning
+            stream.Position = 0;
+
+            // Return the stream as a downloadable Excel file with the specified filename
+            return File(stream, "application/xlsx", fileName);
+
+        }
+
+        public IActionResult Index()
+        {
+            return View();
+        }
+
+        public IActionResult Privacy()
+        {
+            return View();
+        }
+
+        [ResponseCache(Duration = 0, Location = ResponseCacheLocation.None, NoStore = true)]
+        public IActionResult Error()
+        {
+            return View(new ErrorViewModel { RequestId = Activity.Current?.Id ?? HttpContext.TraceIdentifier });
+        }
+    }
+}

Videos/Comments/Data/ClearInput.xlsx

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+namespace Comments.Models
+{
+    public class ErrorViewModel
+    {
+        public string? RequestId { get; set; }
+
+        public bool ShowRequestId => !string.IsNullOrEmpty(RequestId);
+    }
+}

Videos/Comments/Data/CommentsTemplate.xlsx

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+namespace Comments
+{
+    public class Program
+    {
+        public static void Main(string[] args)
+        {
+            var builder = WebApplication.CreateBuilder(args);
+
+            // Add services to the container.
+            builder.Services.AddControllersWithViews();
+
+            var app = builder.Build();
+
+            // Configure the HTTP request pipeline.
+            if (!app.Environment.IsDevelopment())
+            {
+                app.UseExceptionHandler("/Home/Error");
+                // The default HSTS value is 30 days. You may want to change this for production scenarios, see https://aka.ms/aspnetcore-hsts.
+                app.UseHsts();
+            }
+
+            app.UseHttpsRedirection();
+            app.UseStaticFiles();
+
+            app.UseRouting();
+
+            app.UseAuthorization();
+
+            app.MapControllerRoute(
+                name: "default",
+                pattern: "{controller=Home}/{action=Index}/{id?}");
+
+            app.Run();
+        }
+    }
+}

Videos/Comments/Data/DeleteInput.xlsx

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+{
+  "$schema": "http://json.schemastore.org/launchsettings.json",
+  "iisSettings": {
+    "windowsAuthentication": false,
+    "anonymousAuthentication": true,
+    "iisExpress": {
+      "applicationUrl": "http://localhost:48728",
+      "sslPort": 44343
+    }
+  },
+  "profiles": {
+    "http": {
+      "commandName": "Project",
+      "dotnetRunMessages": true,
+      "launchBrowser": true,
+      "applicationUrl": "http://localhost:5072",
+      "environmentVariables": {
+        "ASPNETCORE_ENVIRONMENT": "Development"
+      }
+    },
+    "https": {
+      "commandName": "Project",
+      "dotnetRunMessages": true,
+      "launchBrowser": true,
+      "applicationUrl": "https://localhost:7280;http://localhost:5072",
+      "environmentVariables": {
+        "ASPNETCORE_ENVIRONMENT": "Development"
+      }
+    },
+    "IIS Express": {
+      "commandName": "IISExpress",
+      "launchBrowser": true,
+      "environmentVariables": {
+        "ASPNETCORE_ENVIRONMENT": "Development"
+      }
+    }
+  }
+}