Files with .PST extension represent Outlook Personal Storage Files (also called Personal Storage Table) that store variety of user information. User information is stored in folders of different types that include emails, calendar items, notes, contacts, and several other file formats. PST files are used for archiving emailing data offline that can be later loaded and viewed in various applications.
WebP, introduced by Google, is a modern raster web image file format that is based on lossless and lossy compression. It provides same image quality while considerably reducing the image size. Since most of the web pages use images as effective representation of data, the use of WebP images in web pages results in faster loading of web pages.
You can also convert PST into many other file formats. Please see the complete list below.