You must use third-party software that can combine multiple PST files into one to merge Outlook PST folders into a single folder without using MS Outlook. There are various options available online; however, Sametools PST Merge Software is one of them. Without installing Outlook, you can use this utility to merge Outlook data files into a new PST file. It can merge Outlook emails, calendars, contacts, notes, and so on. The software can merge Outlook PST files from 2019, 2016, 2013, 2010, 2007, and previous versions. It also makes it simple to merge ANSI, Unicode, archived, and password-protected Outlook PST files. Users can store individual PST files on the desktop at a convenient location
