Sadly there does not seem to exist any API to disable the OSK for specific application or controls. Google shows some suggestions like killing the OSK process or disabling registry settings but that does not sound proper thing to do. I was able to prevent it from appearing with some event handling and toggling the controls' ReadOnly property like this -

void SetReadOnly(TextBox tb, bool value)
{
    tb.ReadOnly = value;
    tb.BackColor = Color.Black;
    tb.ForeColor = Color.Black;
    tb.BackColor = Color.White;
}

private void Form1_Load(object sender, EventArgs e)
{
    var vk = new MindFusion.UI.WinForms.VirtualKeyboard();
    vk.Dock = DockStyle.Bottom;
    Controls.Add(vk);
    vk.IsStandAlone = false;
    vk.PreventActivation = true;
    //textBox1.AccessibleRole = AccessibleRole.StaticText;
    //textBox2.AccessibleRole = AccessibleRole.StaticText;

    vk.KeyPressed += Vk_KeyPressed;

    SetReadOnly(textBox1, true);
    SetReadOnly(textBox2, true);

    textBox1.KeyPress += OnTextBoxKeyPress;
    textBox2.KeyPress += OnTextBoxKeyPress;
}


private void OnTextBoxKeyPress(object sender, KeyPressEventArgs e)
{
    var timer = new Timer();
    timer.Interval = 3;
    timer.Tick += (s, a) =>
    {
        SetReadOnly(textBox1, true);
        SetReadOnly(textBox2, true);
        timer.Stop();
    };
    timer.Start();
}

private void Vk_KeyPressed(object sender, MindFusion.UI.WinForms.VirtualKeyEventArgs e)
{
    SetReadOnly(textBox1, false);
    SetReadOnly(textBox2, false);
}
 

I have tested this only on desktop machine with touch screen and win10 tablet mode enabled. You should be able to extend it to support more edit boxes by following currently focused control rather than setting ReadOnly on specific boxes.

Regards,
Slavcho
Mindfusion