Three button click events in c# accessing the same docx

How do I write my code for three buttons on a user form such that:

button 7 loads a word document and opens it,
button 2 is a find button that searches the open document also highlight found matches one after the other as the user chooses which ones to replace,
button 3 is a replace button that does the replacement while the document is open and visible to the user.

Here is what I have so far but I'm unable to get the other two buttons "button 2" and "button 3" to work without the word app opening over and over every time I hit the find button or the replace button.

here is what I have so far:

private void button7_Click(object sender, EventArgs e)
{
if (of.ShowDialog() == DialogResult.OK)
{
textBox7.Text = of.FileName;
object fileName = Path.Combine(System.Windows.Forms.Application.StartupPath, of.FileName);
Microsoft.Office.Interop.Word.Application wordApp1 = new Microsoft.Office.Interop.Word.Application { Visible = true };
Microsoft.Office.Interop.Word.Document aDoc = wordApp1.Documents.Open(ref fileName, ReadOnly: false, Visible: true);
Microsoft.Office.Interop.Word.Find fnd = wordApp1.ActiveWindow.Selection.Find;
}
}
private void button2_Click(object sender, EventArgs e) { }
public void button3_Click(object sender, EventArgs e) { }
private void comboBox3_SelectedIndexChanged(object sender, EventArgs e) { }
}