sample

public void Pick()
        {
            UIDocument uidoc = this.Application.ActiveUIDocument;
            UIApplication uiapp = Application; //UIApplicatio already defined as Application property
            Application app = Application.Application;
            Document doc = Document; //Document already defined as Document property

            StringBuilder sb = new StringBuilder();
            sb.Append(doc.PathName + "\n");
            TaskDialog.Show("Info",sb.ToString());

            Reference elemRef = uidoc.Selection.PickObject(ObjectType.Element);
            ElementId elemId = elemRef.ElementId;
            Element elem = doc.GetElement(elemId);

            TaskDialog.Show("info",elem.Name);
        }