Hi amar,

Refer the below sample function. For this i have used Microsoft.Office.Interop.Excel library.

C#

using Excel = Microsoft.Office.Interop.Excel;

public void ExcelToCSV(string sourceFile,string destinationFile)
{
    Type officeType = Type.GetTypeFromProgID("Excel.Application");
    if (officeType == null)
    {
        ClientScript.RegisterClientScriptBlock(this.GetType(), "", "alert('Excel is not installed in the machine')", true);
    }
    else
    {
        Excel.Application app = new Excel.Application();
        app.DisplayAlerts = false;
        // Open Excel Workbook for conversion.
        Excel.Workbook excelWorkbook = app.Workbooks.Open(sourceFile);
        // Save file as CSV file.
        excelWorkbook.SaveAs(destinationFile, Excel.XlFileFormat.xlCSV);
        // Close the Workbook.
        excelWorkbook.Close();
        // Quit Excel Application.
        app.Quit();
    }
}

VB.Net

Imports Excel = Microsoft.Office.Interop.Excel

Public Sub ExcelToCSV(sourceFile As String, destinationFile As String)
    Dim officeType As Type = Type.GetTypeFromProgID("Excel.Application")
    If officeType Is Nothing Then
        ClientScript.RegisterClientScriptBlock(Me.[GetType](), "", "alert('Excel is not installed')", True)
    Else
        Dim app As New Excel.Application()
        app.DisplayAlerts = False
        ' Open Excel Workbook for conversion.
        Dim excelWorkbook As Excel.Workbook = app.Workbooks.Open(sourceFile)
        ' Save file as CSV file.
        excelWorkbook.SaveAs(destinationFile, Excel.XlFileFormat.xlCSV)
        ' Close the Workbook.
        excelWorkbook.Close()
        ' Quit Excel Application.
        app.Quit()
    End If
End Sub