'system.outofmemoryexception' while opening 300 mega .dbf file

I try to open a 300mg .dbf file in my code, but this error appears '$ exception.Message' threw an exception of type 'System.OutOfMemoryException' , a smaller file of 300kb is opened normally, I know the file is too large, but I also know that it is possible to execute files of this size (300mg)

I'm using Windows Form ...

using System;
using System.Collections.Generic;
using System.ComponentModel;
using System.Data;
using System.Drawing;
using System.Linq;
using System.Text;
using System.Windows.Forms;
using System.Data.OleDb;
using System.Collections;
using System.Threading;

namespace LerDBF
{

public partial class Form1 : Form
{
    public Form1()
    {
        InitializeComponent();
    }

    private void btnConsultaPrimaria_Click(object sender, EventArgs e)
    {
        try
        {
            OleDbConnection oConn = new OleDbConnection();
            oConn.ConnectionString = "Provider = Microsoft.Jet.OLEDB.4.0; Data Source= c:\; Extended Properties = dBASE IV; User ID=; Password=";
            OpenFileDialog openFileDialog1 = new OpenFileDialog();
            openFileDialog1.Filter = "Arquivos DBF|*.dbf";
            openFileDialog1.Title = "Selecione o arquivo DBF";

            if (openFileDialog1.ShowDialog() == System.Windows.Forms.DialogResult.OK)
            {
                oConn.Open();
                OleDbCommand oCmd = oConn.CreateCommand();

                oCmd.CommandText = @"SELECT * FROM " + openFileDialog1.FileName;
                DataTable dt = new DataTable();
                dt.Load(oCmd.ExecuteReader());
                ArrayList dadosComboBox = new ArrayList();
                foreach (DataColumn c in dt.Columns)
                {
                    dadosComboBox.Add(c.ColumnName);
                }
                comboBox1.DataSource = dadosComboBox;
                oConn.Close();
                dataGridView1.DataSource = dt;
            }
        }
        catch (Exception exc)
        {
            MessageBox.Show("Erro: " + exc.Message);
        }
    }

    private void btnConsultaSecundaria_Click(object sender, EventArgs e)
    {
        try
        {
            OleDbConnection oConn = new OleDbConnection();
            oConn.ConnectionString = "Provider = Microsoft.Jet.OLEDB.4.0; Data Source= c:\; Extended Properties = dBASE IV; User ID=; Password=";
            OpenFileDialog openFileDialog1 = new OpenFileDialog();
            openFileDialog1.Filter = "Arquivos DBF|*.dbf";
            openFileDialog1.Title = "Selecione o arquivo DBF";

            if (openFileDialog1.ShowDialog() == System.Windows.Forms.DialogResult.OK)
            {
                oConn.Open();
                OleDbCommand oCmd = oConn.CreateCommand();

                oCmd.CommandText = @"SELECT * FROM " + openFileDialog1.FileName;
                DataTable dt = new DataTable();
                dt.Load(oCmd.ExecuteReader());
                ArrayList dadosComboBox = new ArrayList();
                foreach (DataColumn c in dt.Columns)
                {
                    dadosComboBox.Add(c.ColumnName);
                }
                comboBox2.DataSource = dadosComboBox;
                oConn.Close();
                dataGridView2.DataSource = dt;
            }
        }
        catch (Exception exc)
        {
            MessageBox.Show("Erro: " + exc.Message);
        }
    }
}


}

Would I have to use some thread to run this in the background?