// C# code

// Receiving parameters of visible square
double leftView, topView, widthView, heightView;

axDrawingControl.Window.GetViewRect(out leftView, out topView, out widthView, out heightView);

// Receiving pages parameters
double pageWidth, pageHeight;

Visio.Page page = axDrawingControl.Window.PageAsObj;

pageWidth = page.PageSheet.get_Cells("PageWidth").ResultIU;
pageHeight = page.PageSheet.get_Cells("PageHeight").ResultIU;