If I am reading your question correctly, OWA is a web based application and a .pst file can only be opened by Microsoft Outlook. So, to open the file, the web application will not work. You will need to have Outlook installed on your system. Also, a mistake that many make is to put their .pst files on a network drive or try to do it on a cloud drive. This will hinder Outlook from working properly, especially if you do not have access to the location of the .pst file. Putting it on a cloud drive will not work.