ANSI-formatted .pst files, also known as Outlook 97-2002 Personal Folders Files, were the standard personal folder format for saving data in Outlook for Windows in versions 97-2002. This file format can't be imported into Outlook for Mac.
Beginning with Microsoft Office Outlook 2003, a new Personal Folders file (.pst) format was introduced that supports multilingual Unicode data and offers greater storage capacity for items and folders. Outlook for Mac can import this newer, Unicode version of the Personal Folders file (.pst) format.
If you have the older version of the ANSI-formatted .pst file, there is no automated procedure to convert that file to the newer file format. However, you can create a new Outlook Data File (.pst) in Outlook 2003 (for Windows) or later versions, and then import items from the older file into the new file. You can then import the new .pst file into Outlook for Mac.
For more information about how to create .pst files and importing items, see Help for your version of Outlook for Windows.