If you want to bulk convert PST to PDF, you can download a reliable third-party software. I suggest using
Outlook PST Converter for this purpose. This software can immediately convert Outlook PST files into EML, MSG, MBOX, PDF, TXT, HTML, EMLX, etc. It is the best tool to convert all Outlook PST items such as Email, Calendar, Contacts, Tasks, etc. Try now for free by downloading the demo version. It permits you to evaluate the workability and features of the tool.