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.
Files with .DOT extension are template files created by Microsoft Word to have pre-formatted settings for generation of further DOC or DOCX files. A template file is created in order to have specific user settings that should be applied to subsequent files created from these. These settings include page margins, borders, headers, footers, and other page settings. Such templates are used in official documents such as company letterheads and standardized forms.
You can also convert PST into many other file formats. Please see the complete list below.