NSF and PST both are different file formats for storing mailbox data. Neither Lotus Notes nor Outlook provides any utility for converting NSF database to PST format. But there is a manual trick that can easily export entire Lotus Notes emails to MS Outlook. Through the manual trick you can export Lotus Notes emails to either Comma Separated value or Structured Text format. After exporting NSF file data into these formats to MS Outlook format.
Read more details, here:- http://migrateemails.com/2015/09/03/how-to-convert-outlook-pst-files-into-ibm-notes-nsf-database-file/