PM> Install-Package Spire.XLS 

using Spire.Xls;
using System.Text;

namespace ConvertAWorksheetToCsv
{
    class Program
    {
        static void Main(string[] args)
        {
            //Create an instance of Workbook class
            Workbook workbook = new Workbook();
            //Load an Excel file
            workbook.LoadFromFile("Sample.xlsx");

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

            //Save the worksheet as CSV
            sheet.SaveToFile("ExcelToCSV.csv", ",", Encoding.UTF8);
        }
    }
}

Imports Spire.Xls
Imports System.Text

Namespace ConvertAWorksheetToCsv
    Friend Class Program
        Private Shared Sub Main(ByVal args As String())
            'Create an instance of Workbook class
            Dim workbook As Workbook = New Workbook()
            'Load an Excel file
            workbook.LoadFromFile("Sample.xlsx")

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

            'Save the worksheet as CSV
            sheet.SaveToFile("ExcelToCSV.csv", ",", Encoding.UTF8)
        End Sub
    End Class
End Namespace

using Spire.Xls;

namespace ConvertCsvToExcel
{
    class Program
    {
        static void Main(string[] args)
        {
            //Create an instance of Workbook class
            Workbook workbook = new Workbook();

            //Load a CSV file
            workbook.LoadFromFile(@"ExcelToCSV.csv", ",", 1, 1);

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

            //Access the used range in the worksheet
            CellRange usedRange = sheet.AllocatedRange;
            //Ignore errors when saving numbers in the range as text
            usedRange.IgnoreErrorOptions = IgnoreErrorType.NumberAsText;
            //Autofit columns and rows
            usedRange.AutoFitColumns();
            usedRange.AutoFitRows();

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

Imports Spire.Xls

Namespace ConvertCsvToExcel
    Friend Class Program
        Private Shared Sub Main(ByVal args As String())
            'Create an instance of Workbook class
            Dim workbook As Workbook = New Workbook()

            'Load a CSV file
            workbook.LoadFromFile("ExcelToCSV.csv", ",", 1, 1)

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

            'Access the used range in the worksheet
            Dim usedRange As CellRange = sheet.AllocatedRange
            'Ignore errors when saving numbers in the range as text
            usedRange.IgnoreErrorOptions = IgnoreErrorType.NumberAsText
            'Autofit columns and rows
            usedRange.AutoFitColumns()
            usedRange.AutoFitRows()

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

PM> Install-Package Spire.XLS

using Spire.Xls;

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

            //Load an Excel document
            workbook.LoadFromFile(@"C:\Users\Administrator\Desktop\sample.xlsx");

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

            //Freeze the top row
            sheet.FreezePanes(2, 1);

            //Save to another file
            workbook.SaveToFile("FreezeTopRow.xlsx", ExcelVersion.Version2016);
        }
    }
}

Imports Spire.Xls
 
Namespace FreezeTopRow
    Class Program
        Shared  Sub Main(ByVal args() As String)
            'Create a Workbook instance
            Dim workbook As Workbook =  New Workbook() 
 
            'Load an Excel document
            workbook.LoadFromFile("C:\Users\Administrator\Desktop\sample.xlsx")
 
            'Get the first worksheet
            Dim sheet As Worksheet =  workbook.Worksheets(0) 
 
            'Freeze the top row
            sheet.FreezePanes(2, 1)
 
            'Save to another file
            workbook.SaveToFile("FreezeTopRow.xlsx", ExcelVersion.Version2016)
        End Sub
    End Class
End Namespace

using Spire.Xls;

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

            //Load an Excel document
            workbook.LoadFromFile(@"C:\Users\Administrator\Desktop\sample.xlsx");

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

            //Freeze the first column
            sheet.FreezePanes(1, 2);

            //Save to another file
            workbook.SaveToFile("FreezeFirstColumn.xlsx", ExcelVersion.Version2016);
        }
    }
}

Imports Spire.Xls
 
Namespace FreezeFirstColumn
    Class Program
        Shared  Sub Main(ByVal args() As String)
            'Create a Workbook instance
            Dim workbook As Workbook =  New Workbook() 
 
            'Load an Excel document
            workbook.LoadFromFile("C:\Users\Administrator\Desktop\sample.xlsx")
 
            'Get the first worksheet
            Dim sheet As Worksheet =  workbook.Worksheets(0) 
 
            'Freeze the first column
            sheet.FreezePanes(1, 2)
 
            'Save to another file
            workbook.SaveToFile("FreezeFirstColumn.xlsx", ExcelVersion.Version2016)
        End Sub
    End Class
End Namespace

using Spire.Xls;

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

            //Load an Excel document
            workbook.LoadFromFile(@"C:\Users\Administrator\Desktop\sample.xlsx");

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

            //Freeze the first row and the first column
            sheet.FreezePanes(2, 2);

            //Save to another file
            workbook.SaveToFile("FreezeFirstRowAndFirstColumn.xlsx", ExcelVersion.Version2016);
        }
    }
}

Imports Spire.Xls
 
Namespace FreezeFirstRowAndFirstColumn
    Class Program
        Shared  Sub Main(ByVal args() As String)
            'Create a Workbook instance
            Dim workbook As Workbook =  New Workbook() 
 
            'Load an Excel document
            workbook.LoadFromFile("C:\Users\Administrator\Desktop\sample.xlsx")
 
            'Get the first worksheet
            Dim sheet As Worksheet =  workbook.Worksheets(0) 
 
            'Freeze the first row and the first column
            sheet.FreezePanes(2, 2)
 
            'Save to another file
            workbook.SaveToFile("FreezeFirstRowAndFirstColumn.xlsx", ExcelVersion.Version2016)
        End Sub
    End Class
End Namespace