Excel documents using the Office Open XML format (xlsx) can be filled without AddIn (since ProOffice version 4.0).
In general it is recommend to install the AddIn by a software distribution.
If any Excel application is used, when ProOffice is installing the ProNovia SAPtoExcel AddIn it may lead to an error.
The AddIn will only be installed once (or after an up-date). If the error occurred, all Excel applications must be closed and the automatic filling (or Installation) must be repeated.