InfoPath Dev

Infopath 2007, trying to follow the instructions listed here:

 http://msdn.microsoft.com/en-us/library/ms812501.aspx

// User is done signing -- lock down the control.
inkPicture1.InkEnabled = false;

My newbie question and forgive me if it's painfully obvious and I'm missing it...but the instructions start with the control already captured in an object.  How do I get a handle of the control?  Do I need to add a Reference?  

I tried

XPathNavigator, root, inkPic;

root = this.MainDataSource.CreateNavigator();

inkPic = root.SelectSingleNode(<XPath Source> , NamespaceManager);

// I get a handle of the control, but when I try this

inkPic.InkEnabled = false; 

// I get this error -  System.Xml.XPath.XPathNavigator does not contain a definition for 'InkEnabled'
Thanks for any help.