You can use this PST Merger Software if you want to Merge PST files in One file. this Software easily Merge your multiple PST files without any file size limit. It is the safe and secure tool which can effectively merge your multiple PST file into one PST file. It can merge any size of PST file, join password protected in Outlook PST file. It is a simple PST merge tool that does not require special IT knowledge.
You can also try Merge PST Tool to merge multiple PST files in MS-Outlook. It Combines PST files without any duplicates PST items. It Consolidates various PST files such as Emails, Contacts, Calendars, Tasks, Notes, and all. It merges without any duplicates PST files in MS-Outlook. Demo Version is also available. Supports in all Version of Windows and Outlook. Capable in ANSI and also UNICODE formats. Visit here for more info:-https://www.betavare.com/merge-pst/