OLM and PST both are different file formats for storing mailbox data. Neither Mac Outlook nor Windows MS Outlook provide any free utility for conversion of OLM to PST. But there is a manual trick that can easily export entire OLM file data to PST format. Through the manual trick you first export the OLM file data to IMAP mail account then move all IMAP mailbox data to Outlook PST format.
For more details see this blog:- migrateemails.com/2015/09/22/make-olm-to-pst-conversion-easy-instant-and-accurate/