In the Contacts folder, select EXPORT from the toolbar.
I would use the CSV format (text file, fields separated by commas). This is a virtually universal format.
In Outlook - File, Import Export, Import From another program, CSV
NOTE:
Outlook, for inexplicable MS reasons, will make two DIFFERENT versions of filename.PST (Outlook.psts default). If you export from within Outlook, you get a lesser inclusive file. If you close Outlook and copy the file manually (%userprofile%\appdata\ ... filename.pst) you will get everything - mail, contacts, calendar etc.