in carboxylic acid: Hydroxy and keto acids. ...not the same. The 2-hydroxy acids form cyclic dimeric esters (formed by the esterification of two molecules of the acid) called lactides, whereas the 3- and 4-hydroxy acids undergo intramolecular esterification to give cyclic esters called lactones.
VBA's ActiveWorkbook property refers to the workbook with the focus. The active workbook may or may not contain the code that's referencing the active workbook, which is an important distinction. It's perfectly acceptable to use this property to reference the active workbook from code inside the active workbook.
I guess You will have to create a workbook. If you want to use an already open excel then you should not create an instance of excel but call Marshal.GetActiveObect and pass the progId. ex: objApp = Marshal.GetActiveObject(Excel.Application) and then use activeworkbook you would get the active work book.