Microsoft.Office.Interop.Excel.ApplicationClass excelObj = new Microsoft.Office.Interop.Excel.ApplicationClass();
Microsoft.Office.Interop.Excel.Workbook workBookObj = null;
workBookObj = excelObj.Workbooks.Open(fileName, Missing.Value, Missing.Value,Missing.Value, Missing.Value, Missing.Value, Missing.Value, Missing.Value,Missing.Value, Missing.Value, Missing.Value, Missing.Value, Missing.Value, Missing.Value, Missing.Value);
foreach (Microsoft.Office.Interop.Excel.Worksheet sheet in workBookObj.Sheets)
{
sheet.Name
}