Where you are using the mail merge functions of Pathways the documents are created and merged to Microsoft Word format.
These mail merge templates are Microsoft's DOCX format, which can be opened and managed using any fully patched and updated version of Office starting with Office 2010.
Similarly we use Microsoft Excel for reports and exports as it provides the most usable method of delivering the source data for uses outside Pathways. As with the Mail Merge documents, these are a XLSX format and requires Office 2010 or later.
RECOMMENDED OFFICE VERSION?
Our experience to date has been that Office 2013 is the most stable release of Office for mail merge and Excel reporting, however from mid 2016 onwards, Office 2016 is maturing into a more release-worthy and stable option.