If any users searching the best and easy solution of Combine Multiple PST files into one PST files then I would suggest the KDETools PST Merge. It merges several PST items in Outlook such as Emails, Contacts, Calendars, Tasks and all without any duplicates PST files. It merges PST files in all Version of Windows and Outlook. No needs MS-Outlook installation. Free Version is an option in this tool. Only selected PST files merged.
More Info: https://www.kdetools.com/pst-merge.html
If you have multiple PST files and you want to merge them in one PST file, try PST Merge Tool to easily complete this task with a simple mouse click. It supports both ANSI and UNICODE PST file and merges multiple PST files in one PST file without any data loss.
Visit here for more info: https://www.osttopstapp.com/pst-merge.html
If you need to combine Outlook PST data then rendering my opinion you can try Merge PST Tool who is third-party software. With the help of this application, you can rapidly and securely merge to your all kind, size data in few minutes. There is a security of data combines so don’t worry, first you can try the trial version to this utility.