C#

Form newForm = new Form();
newForm.TopLevel = false;
newForm.Parent = this;
newForm.Visible = true;
newForm.Location = new Point(10, 10);
this.Controls.Add(newForm);

I are troll

NativeWindow wnd = new NativeWindow(new CreateParams()
    {
        Parent = rightHandPanel.Handle,
        Height = rightHandPanel.Height,
        Width = rightHandPanel.Width,
        X = Y = 0
    }
Form display = formYouWantToDisplay;

wnd.CreateHandle();
display.Show(wnd);    //This works because NativeWindow implements IWin32Window

private void button1_Click(object sender, EventArgs e)
{
   TabPage newTabPage = new TabPage("Form " + tabControl1.TabPages.Count);
   newTabPage.Size = new Size(tabControl1.Width, tabControl1.Height);
   Form2 newForm = new Form2();
   newForm.TopLevel = false;
   newForm.Parent = this;
   newForm.Visible = true;
   newForm.Location = newTabPage.Location;
   newForm.Location = new Point(3, 3);
   newForm.Size = new Size(newTabPage.Width - 3, newTabPage.Height - 3);
   newForm.FormBorderStyle = FormBorderStyle.None;
   newTabPage.Controls.Add(newForm);
   tabControl1.TabPages.Add(newTabPage);
}

private void button1_Click(object sender, EventArgs e)
{
   TabPage tab = this.Parent as TabPage;
   TabControl tabControl = tab.Parent as TabControl;
   tabControl.TabPages.Remove(tab);
   this.Dispose();
}

void RetrieveData()
{
    Stream bookStream = new FileStream("books.txt", FileMode.OpenOrCreate);

    using(StreamReader booksReader = new StreamReader(bookStream))
    {
        //Do what you want with booksReader here, the using block will automatically close the streams to avoid memory leaks
    }
}