If you have PST file of ANSI and you want to convert it into Unicode PST for some reasons, then try PST Upgrade tool
Outlook 2000 and earlier version support work on ANSI and uses the ANSI format to store data into PST file but with outlook 2003 Microsoft started using UNICODE format for storing data into PST file. Outlook 2003 and later version does support ANSI version of Outlook for backwards compatibility reasons, but you can't open UNICODE outlook PST Outlook 2000.
The PST Upgrade and downgrade is a tool which let you convert your ANSI PST to UNICODE PST and UNICODE PST to ANSI PST conversion with the most professional manner.
* Below options must be installed in order to flawlessly operate Shoviv software
Operating System (32 or 64 bit): Windows 10/8.1/8/7/Vista/XP, Windows Server 2003/2008/2008 R2/2012/2012 R2/2016 (Any of them)
Hard Disk: Minimum 100 MB of free hard disk space
Processor: Minimum 1 GHz Processor (2.4 GHz is recommended)
RAM: Minimum 512 MB of RAM (1 GB is recommended)
MS Outlook (32 or 64 bit): Outlook 2000, 2003, 2007, 2010, 2013 or 2016 versions.(Outlook 2013 is recommended)