.ZPI File Extension

Index file used by PDF Converter, a plug-in program used with popular applications for managing, creating, and converting .PDF files; contains a searchable index of PDF files; enables searching within large collections of PDF files.

Zip file created using Zip compression, but with a renamed file extension; commonly used to rename a .ZIP file extension for an email attachment in order to pass through an email filter.

ZPI files, once received, can be renamed back to the original ".zip" extension and then opened.