internal static DataTable GetExcelSheet(string excelFile,string sheetName = "")
{
    string fullPathToExcel = Path.GetFullPath(excelFile);
    string connString = string.Format("Provider=Microsoft.ACE.OLEDB.12.0;Data Source={0};Extended Properties='Excel " + (excelFile.ToLower().EndsWith("x") ? "12.0" : "8.0") + ";HDR=yes'", fullPathToExcel);
    return GetDataTable(connString, "SELECT * FROM [" + (string.IsNullOrEmpty(sheetName) ? GetTableName(connString, 0) : sheetName + "$") + "]");
}

private static DataTable GetDataTable(string connectionString, string sql)
{
    DataTable dt = new DataTable();

    using (OleDbConnection conn = new OleDbConnection(connectionString))
    {
        conn.Open();
        using (OleDbCommand cmd = new OleDbCommand(sql, conn))
        {
            using (OleDbDataReader rdr = cmd.ExecuteReader())
            {
                dt.Load(rdr);
                return dt;
            }
        }
    }
}
private static string GetTableName(string connectionString, int row = 0)
{
    OleDbConnection conn = new OleDbConnection(connectionString);
    try
    {
        conn.Open();
        return conn.GetSchema("Tables").Rows[row]["TABLE_NAME"] + "";
    }
    catch { }
    finally { conn.Close();}
    return "sheet1";
}