Outlook saves your data files depends on the version of Outlook you’re running. By default, Outlook 2007 and 2010 store OST files in your AppData folder at the following location:
Starting with Outlook 2013, the location of OST files moved to the Documents folder. Outlook 2013 and 2016 now store PST files at the following location:
You can use Import/Export option of Microsoft Outlook to convert OST to PST format.