CODE EXAMPLE FOR CSHARP

edit opened excel file directly

try
            {
                xlApp = (Excel.Application)System.Runtime.InteropServices.Marshal.GetActiveObject("Excel.Application");
            }
            catch (Exception ex)
            {
                if (ex.ToString().Contains("0x800401E3 (MK_E_UNAVAILABLE)"))
                {
                    xlApp = new Excel.Application();
                }
                else
                {
                    throw;
                }
            }