Where is the getDocument method for Vb.net or C#?

I’m new at LibreOffice. Currently I have a task to use Microsoft Studio .Net
to create/manage a LibreOffice Calc . I use the example from official website named as “ViewSample.cs” , but system always shows me : can’t find getDocument not in content .
Is there any where I need to include or set up ? I’ve included api for my .Net project . Thank you .