INFO: What is a .pst File?
.PST files are commonly used as both the storage and backup format for Outlook files, and can be password protected as well as encrypted to protect sensitive information. The .pst format is also commonly referred to as a Personal Folder File.
Outlook may create many .pst files for different purposes or folders that are created within Outlook. Most commonly there will be one Outlook.pst file and one Archive.pst file.