PM> Install-Package Spire.XLS

using Spire.Xls;
using System.Drawing;

namespace ApplySuperscriptAndSubscript
{
    internal class Program
    {
        static void Main(string[] args)
        {
            //Create a Workbook object
            Workbook workbook = new Workbook();

            //Get the first worksheet
            Worksheet sheet = workbook.Worksheets[0];

            //Add text to specific cells
            sheet.Range["B2"].Text = "This is an example of subscript:";
            sheet.Range["D2"].Text = "This is an example of superscript:";

            //Add rich text to a specific cell
            CellRange range = sheet.Range["B3"];
            range.RichText.Text = "an = Sn - Sn-1";

            //Create a custom font
            ExcelFont font = workbook.CreateFont();
            //Enable the subscript property of the font
            font.IsSubscript = true;
            //Set font color
            font.Color = Color.Green;
            //Assign the font to specific characters of the rich text in the cell
            range.RichText.SetFont(6, 6, font);
            range.RichText.SetFont(11, 13, font);

            //Add rich text to a specific cell
            range = sheet.Range["D3"];
            range.RichText.Text = "a2 + b2 = c2";

            //Create a custom font
            font = workbook.CreateFont();
            //Enable the superscript property of the font
            font.IsSuperscript = true;
            //Assign the font to specific characters of the rich text in the cell
            range.RichText.SetFont(1, 1, font);
            range.RichText.SetFont(6, 6, font);
            range.RichText.SetFont(11, 11, font);

            //Auto-fit column widths
            sheet.AllocatedRange.AutoFitColumns();

            //Save the result file
            workbook.SaveToFile("ApplySubscriptAndSuperscript.xlsx", ExcelVersion.Version2013);
            workbook.Dispose();
        }
    }
}

Imports Spire.Xls
Imports System.Drawing

Namespace ApplySuperscriptAndSubscript
    Friend Class Program
        Private Shared Sub Main(ByVal args As String())
            'Create a Workbook object
            Dim workbook As Workbook = New Workbook()

            'Get the first worksheet.
            Dim sheet As Worksheet = workbook.Worksheets(0)

            'Add text to specific cells
            sheet.Range("B2").Text = "This is an example of subscript:"
            sheet.Range("D2").Text = "This is an example of superscript:"

            'Add rich text to a specific cell
            Dim range As CellRange = sheet.Range("B3")
            range.RichText.Text = "an = Sn - Sn-1"

            'Create a custom font
            Dim font As ExcelFont = workbook.CreateFont()
            'Enable the subscript property of the font
            font.IsSubscript = True
            'Set font color
            font.Color = Color.Green
            'Assign the font to specific characters of the rich text in the cell
            range.RichText.SetFont(6, 6, font)
            range.RichText.SetFont(11, 13, font)

            'Add rich text to a specific cell
            range = sheet.Range("D3")
            range.RichText.Text = "a2 + b2 = c2"

            'Create a custom font
            font = workbook.CreateFont()
            'Enable the superscript property of the font
            font.IsSuperscript = True
            'Assign the font to specific characters of the rich text in the cell
            range.RichText.SetFont(1, 1, font)
            range.RichText.SetFont(6, 6, font)
            range.RichText.SetFont(11, 11, font)

            'Auto-fit column widths
            sheet.AllocatedRange.AutoFitColumns()

            'Save the result file
            workbook.SaveToFile("ApplySubscriptAndSuperscript.xlsx", ExcelVersion.Version2013)
            workbook.Dispose()
        End Sub
    End Class
End Namespace

PM> Install-Package Spire.Doc

using Spire.Doc;
using Spire.Doc.Documents;
using Spire.Doc.Fields;

namespace ExtractTextFromTextbox
{
    class Program
    {
        static void Main(string[] args)
        {
            // Create a Document object
            Document document = new Document();

            // Load a Word file
            document.LoadFromFile("C:\\Users\\Administrator\\Desktop\\Input.docx");

            // Get a specific textbox
            TextBox textBox = document.TextBoxes[0];

            // Create a StreamWriter to write extracted text to a txt file
            using (StreamWriter sw = File.CreateText("result.txt"))
            {
                // Iterate though child objects of the textbox
                foreach (DocumentObject objt in textBox.ChildObjects)
                {
                    // Determine if the child object is a paragraph
                    if (objt.DocumentObjectType == DocumentObjectType.Paragraph)
                    {
                        // Write paragraph text to the txt file
                        sw.Write((objt as Paragraph).Text);
                    }

                    // Determine if the child object is a table
                    if (objt.DocumentObjectType == DocumentObjectType.Table)
                    {
                        // Extract text from table to the txt file
                        ExtractTextFromTable(objt as Table, sw);
                    }
                }

            }
 
        }

        // Extract text from a table
        static void ExtractTextFromTable(Table table, StreamWriter sw)
        {
            for (int i = 0; i < table.Rows.Count; i++)
            {
                TableRow row = table.Rows[i];
                for (int j = 0; j < row.Cells.Count; j++)
                {
                    TableCell cell = row.Cells[j];
                    foreach (Paragraph paragraph in cell.Paragraphs)
                    {
                        sw.Write(paragraph.Text);
                    }
                }
            }
        }
    }
}

using Spire.Doc;
using Spire.Doc.Documents;
using Spire.Doc.Fields;

namespace UpdateTextbox
{
    class Program
    {
        static void Main(string[] args)
        {
            // Create a Document object
            Document document = new Document();

            // Load a Word file
            document.LoadFromFile("C:\\Users\\Administrator\\Desktop\\Input.docx");

            // Get a specific textbox
            TextBox textBox = document.TextBoxes[0];

            // Remove child objects of the textbox
            textBox.ChildObjects.Clear();

            // Add a new paragraph to the textbox
            Paragraph paragraph = textBox.Body.AddParagraph();

            // Set line spacing
            paragraph.Format.LineSpacing = 15f;

            // Add text to the paragraph
            TextRange textRange = paragraph.AppendText("The text in this textbox has been updated.");

            // Set font size
            textRange.CharacterFormat.FontSize = 15f;

            // Save the document to a different Word file
            document.SaveToFile("UpdateTextbox.docx", FileFormat.Docx2019);

            // Dispose resources
            document.Dispose();
        }

    }

}