Most experts say that the best way to shrink a PST file is to use a professional DataVare PST compress tool. There is a Compact tool in Microsoft Outlook that can help you shrink your PST file without having to run any other programs. You need to change the size of your Outlook folder before you can start to reduce the size of your PST file. A PST file can be worked on by more than one person at the same time. Different versions of Microsoft Outlook should all be able to open PST files, whether they are in ANSI or Unicode.