Interact with Excel in Cell level

Microsoft.Office.Interop.Excel.Application app = new Microsoft.Office.Interop.Excel.Application();
app.Workbooks.Open(oldPath, Missing.Value, 1, Missing.Value, Missing.Value, Missing.Value, Missing.Value, Missing.Value, Missing.Value, Missing.Value, Missing.Value, Missing.Value, Missing.Value, Missing.Value, Missing.Value);
Workbook wb = app.ActiveWorkbook;
Worksheet ws = (Worksheet)wb.ActiveSheet;
ws.Columns.AutoFit();
//ws.Cells.get_Range(ws.Cells[1, 1], ws.Cells[1, 2]).Merge(false);
ws.SaveAs(newPath, XlFileFormat.xlExcel9795, Missing.Value, Missing.Value, Missing.Value, Missing.Value,Missing.Value, Missing.Value, Missing.Value, Missing.Value);
app.Workbooks.Close();
System.Runtime.InteropServices.Marshal.ReleaseComObject(ws);
ws = null;
System.Runtime.InteropServices.Marshal.ReleaseComObject(wb);
wb = null;
System.Runtime.InteropServices.Marshal.ReleaseComObject(app);
app = null;
GC.Collect();
GC.WaitForPendingFinalizers();
GC.Collect();