This article explains how to open and search multiple .pst or .ost files without Outlook at once. Any .pst or .ost file (archive, password protected or encrypted) can be searched together with any others. This means that if you're searching for a sensitive email, private contact or calendar item, but you're not certain which file or account you put it in, you'll be able to find it easily with a single search.
Open PST Viewer (pstwalker.exe), make sure that .pst/.ost data files that you want to search are open (if they are, you'll see them all in the All Folders Pane). Select All Mail Items as the location for your search, choose Advanced search option and then type the search criteria that you want to search.
Sort your search results and filter using the Quick grid view search or an Excel-like filtering interface.
1. Quick grid view search. Search text in the visible grid columns and draws a highlight box around any substring that matches its given text.
2. An Excel-like filtering interface. Right click on a column's header, a "Filtering" menu item will be presented. This will let the user select one or more distinct values from that column. When click "Apply", only those rows that have one of the chosen values for that column will be displayed.