PM> Install-Package Spire.XLS

using Spire.Xls;

namespace ConvertHtmlToExcel
{
    internal class Program
    {
        static void Main(string[] args)
        {
            // Specify the input HTML file path
            string filePath = @"C:\Users\Administrator\Desktop\Sample.html";

            // Create an object of the workbook class
            Workbook workbook = new Workbook();

            // Load the HTML file
            workbook.LoadFromHtml(filePath);

            // Save the HTML file in Excel XLSX format
            string result = @"C:\Users\Administrator\Desktop\ToExcel.xlsx";
            workbook.SaveToFile(result, ExcelVersion.Version2013);

            workbook.Dispose();
        }
    }
}

using Spire.Xls;

namespace InsertHtmlStringInExcel
{
    internal class Program
    {
        static void Main(string[] args)
        {
            // Create an object of the workbook class
            Workbook workbook = new Workbook();
            // Get the first sheet
            Worksheet sheet = workbook.Worksheets[0];

            // Specify the HTML string
            string htmlCode = "<p><font size='12'>This is a <b>paragraph</b> with <span style='color: red;'>colored text</span>.</font></p>";

            // Get the cell that you want to add the HTML string to
            CellRange range = sheet.Range["A1"];
            // Add the HTML string to the cell
            range.HtmlString = htmlCode;

            // Auto-adjust the width of the first column based on its content
            sheet.AutoFitColumn(1);

            // Save the resulting workbook to a new file
            string result = @"C:\Users\Administrator\Desktop\InsertHtmlStringIntoCell.xlsx";
            workbook.SaveToFile(result, ExcelVersion.Version2013);

            workbook.Dispose();
        }
    }
}

PM> Install-Package Spire.Presentation

using Spire.Presentation;

namespace ReplaceFirstTextOccurrenceInPPT
{
    class Program
    {
        static void Main(string[] args)
        {
            //Create a Presentation instance
            Presentation ppt = new Presentation();
            //Load a PowerPoint document
            ppt.LoadFromFile("Sample.pptx");

            //Loop through all slides in the document
            foreach (ISlide slide in ppt.Slides)
            {
                //Replace the first occurrence of "Spire.Presentation for .NET" with "E-iceblue Product"
                slide.ReplaceFirstText("Spire.Presentation for .NET", "E-iceblue Product", false);
                break;
            }

            //Save the result document
            ppt.SaveToFile("ReplaceFirstTextOccurrence.pptx", FileFormat.Pptx2013);

        }
    }
}

Imports Spire.Presentation

Namespace ReplaceFirstTextOccurrenceInPPT
    Friend Class Program
        Private Shared Sub Main(ByVal args As String())
            'Create a Presentation instance
            Dim ppt As Presentation = New Presentation()
            'Load a PowerPoint document
            ppt.LoadFromFile("Sample.pptx")

            'Loop through all slides in the document
            For Each slide As ISlide In ppt.Slides
                'Replace the first occurrence of "Spire.Presentation for .NET" with "E-iceblue Product"
                slide.ReplaceFirstText("Spire.Presentation for .NET", "E-iceblue Product", False)
                Exit For
            Next

            'Save the result document
            ppt.SaveToFile("ReplaceFirstTextOccurrence.pptx", FileFormat.Pptx2013)

        End Sub
    End Class
End Namespace

*using Spire.Presentation;

namespace ReplaceAllTextOccurrencesInPPT
{
    class Program
    {
        static void Main(string[] args)
        {
            //Create a Presentation instance
            Presentation ppt = new Presentation();
            //Load a PowerPoint document
            ppt.LoadFromFile("Sample.pptx");

            //Loop through all slides in the document
            foreach (ISlide slide in ppt.Slides)
            {
                //Replace all occurrences of "Spire.Presentation for .NET" with "E-iceblue Product"
                slide.ReplaceAllText("Spire.Presentation for .NET", "E-iceblue Product", false);
            }

            //Save the result document
            ppt.SaveToFile("ReplaceAllTextOccurrences.pptx", FileFormat.Pptx2013);

        }
    }
}

Imports Spire.Presentation

Namespace ReplaceAllTextOccurrencesInPPT
    Friend Class Program
        Private Shared Sub Main(ByVal args As String())
            'Create a Presentation instance
            Dim ppt As Presentation = New Presentation()
            'Load a PowerPoint document
            ppt.LoadFromFile("Sample.pptx")

            'Loop through all slides in the document
            For Each slide As ISlide In ppt.Slides
                'Replace all occurrences of "Spire.Presentation for .NET" with "E-iceblue Product"
                slide.ReplaceAllText("Spire.Presentation for .NET", "E-iceblue Product", False)
            Next

            'Save the result document
            ppt.SaveToFile("ReplaceAllTextOccurrences.pptx", FileFormat.Pptx2013)

        End Sub
    End Class
End Namespace

using Spire.Presentation;
using System.Text.RegularExpressions;

namespace ReplaceTextUsingRegexInPPT
{
    class Program
    {
        static void Main(string[] args)
        {
            //Create a Presentation instance
            Presentation ppt = new Presentation();
            //Load a PowerPoint document
            ppt.LoadFromFile("Sample1.pptx");

            //Loop through all slides in the document
            foreach (ISlide slide in ppt.Slides)
            {
                //Loop through all shapes on each slide
                foreach (IShape shape in slide.Shapes)
                {
                    //Replace text starting with # on the slide to "Monitor"
                    shape.ReplaceTextWithRegex(new Regex(@"\#\w+\b"), "Monitor");
                }
            }

            //Save the result document
            ppt.SaveToFile("ReplaceTextUsingRegex.pptx", FileFormat.Pptx2013);
        }
    }
}

Imports Spire.Presentation
Imports System.Text.RegularExpressions

Namespace ReplaceTextUsingRegexInPPT
    Friend Class Program
        Private Shared Sub Main(ByVal args As String())
            'Create a Presentation instance
            Dim ppt As Presentation = New Presentation()
            'Load a PowerPoint document
            ppt.LoadFromFile("Sample1.pptx")

            'Loop through all slides in the document
            For Each slide As ISlide In ppt.Slides
                'Loop through all shapes on each slide
                For Each shape As IShape In slide.Shapes
                    'Replace text starting with # on the slide to "Monitor"
                    shape.ReplaceTextWithRegex(New Regex("\#\w+\b"), "Monitor")
                Next
            Next

            'Save the result document
            ppt.SaveToFile("ReplaceTextUsingRegex.pptx", FileFormat.Pptx2013)
        End Sub
    End Class
End Namespace