var strConn = "Provider=Microsoft.Jet.OLEDB.4.0;Data Source=" + _fileName + ";Extended Properties=\"Excel 8.0;HDR="Yes";IMEX=0\"";
using (var conn = new OleDbConnection(strConn))
{
DataSet output = new DataSet();

conn.Open();
DataTable schemaTable = conn.GetOleDbSchemaTable(OleDbSchemaGuid.Tables, null);

 foreach (DataRow schemaRow in schemaTable.Rows) {
                    string sheet = schemaRow["TABLE_NAME"].ToString();
                   
                            var cmd = new OleDbCommand("SELECT * FROM [" + sheet + "]", conn)
                            {
                                CommandType = CommandType.Text
                            };
                            var outputTable = new DataTable(sheet);
                            output.Tables.Add(outputTable);
                            new OleDbDataAdapter(cmd).Fill(outputTable);
}