If you want to reduce the size of PST file then try split PST tool beacuse by comprss the size of a PST file you will not able to recover your PST fille in future. So here i suggest you to use KDETools Outlook PST Splitter tool which can split large Oversize PST file into manageable and smaller Outlook PST files as per the Specific Criteria like

Split by Size,
Split by date,
Split by folder
Split by email id

This advanced Outlook PST Splitter software 100% helps the users to work with many versions of MS Outlook as well as it is well compatible with different versions of Windows OS.