I am moving this to the ProcessBook folder, as this seems to be more apropriate.
If you are asking how to automate PB from an external C# code instead of VBA from inside PB, here is a snippet:
PBObjLib.Application pbApp = new PBObjLib.Application();
PBObjLib.Display pbDisplay = pbApp.Displays.Add("Test");
PBSymLib.Trend pbTrend = (PBSymLib.Trend)pbDisplay.Symbols.Add(PBObjLib.pbSYMBOLTYPE.pbSymbolTrend,null);
just a note, no PI SDK invovled, you need a reference to OSIsoft.PBObjLib and OSIsoft.PBSymLib.
@Anthony B. McKay: just curious, did Andreas' solution addressed your question?