Hi Dave,

Thanks for your post!!

Based on my understanding, you p/invoke unmanaged HTML Help API to
implement the F1 help function in your application. But currently, you want
to display the CHM file window as a Child window of your MDI parent window.
If I misunderstand you, please feel free to tell me. Thanks

.Net provided a managed substitution for this, which is named HelpProvider
component. We may leverage this component to get the F1 help function.

Now, for your MDI child window issue, I think this is not build-in
supported. There is no interface for us to explicit make a Html Help Viewer
as the MDI child window. Normally, I think we have 2 workaround options for
it:

#1, Intercept the F1 key event in our MDI app, dynamically decompile the
CHM file, then display the decompiled html pages in a customized editor,
while we can make this customized editor a MDI child window. Maybe we can
use a webbrowser to display the decompiled html pages. This is what many
MDI applicaiton do in their application.
#2, After the CHM file is displayed, we explicitly find this CHM window,
change its window style as MDI child and set its parent to our MDI parent
window. For this way, I have writen a little sample:

private void Form1_Load(object sender, System.EventArgs e)
{
    Form f=new Form();
    f.MdiParent=this;
    f.Show();
    this.KeyPreview=true;
}

[DllImport("user32.dll")]
static extern IntPtr FindWindow(string lpClassName, string lpWindowName);
[DllImport("user32.dll")]
static extern int SetWindowLong(IntPtr hWnd, int nIndex, int dwNewLong);
[DllImport("user32.dll")]
static extern int GetWindowLong(IntPtr hWnd, int nIndex);
[DllImport("user32.dll")]
static extern IntPtr SetParent(IntPtr hWndChild, IntPtr hWndNewParent);

private const int GWL_EXSTYLE=-20;
private const int GWL_STYLE=-16;
private const int WS_EX_MDICHILD=0x00000040;
private const int WS_CHILD=0x40000000;
private void Form1_KeyUp(object sender, System.Windows.Forms.KeyEventArgs e)
{
    if(e.KeyData==Keys.F1)
    {
        System.Diagnostics.Process.Start(@"D:\Course ware\Programingwidnows.chm");
        System.Threading.Thread.Sleep(500);
        IntPtr hCHMWnd=FindWindow("HH Parent", "Programming Windows, Fifth
Edition");
        if(!hCHMWnd.Equals(IntPtr.Zero))
        {
            SetWindowLong(hCHMWnd, GWL_STYLE,
                GetWindowLong(hCHMWnd, GWL_STYLE)|WS_CHILD);
            SetWindowLong(hCHMWnd, GWL_EXSTYLE,
                GetWindowLong(hCHMWnd, GWL_EXSTYLE)|WS_EX_MDICHILD);
            SetParent(hCHMWnd, this.Handle);
        }
        else
        {
            MessageBox.Show("Can not find the CHM file!!");
        }
    }
}
Hope this helps.
============================================
Thank you for your patience and cooperation. If you have any questions or
concerns, please feel free to post it in the group. I am standing by to be
of assistance.

Best regards,
Jeffrey Tan
Microsoft Online Partner Support