Use FindWindow, SetForeGroundWindow And SendKeys

I need to send two keys (" " and {Enter}) to a security warning in an Acrobat Window from a VB.NET application. Here is the function I use :

Private Sub SendAcroKey()
Dim HWND As IntPtr
HWND = FindWindow("Adobe Acrobat", vbNullString)

[Code]....

But I can't get FindWindow() to work properly, it always returns "0". I guess I'm not giving the good parameters, lpClassName and lpWindowName, but I dont now how to get the right ones. So here is the question : How can I know the lpClassName and lpWindowName of a security warning in Adobe Acrobat 7 professional ???

I really have to work this out but theres not much information on the web about those function, even on MSDN.