A Quaestor project file (*.QPF3) contains all project data and solutions which works in combination with a specific knowledge base (there is a hard relation between a project file and the knowledge base in which the project was created).
A project file enables full traceability of a specific project and the possibility (within some limits) to continuously improve a knowledge based application (because knowledge and data have been managed separately).
Knowledge based application
The project file has a more dynamic character than the knowledge base file. It contains specific data and solutions valid within your specific project, while applying/using a specific (knowledge based) application.
Quaestor (.exe) + Knowledge base (.qkb3)+ Project (.qpf3) = (knowledge based) application: A combination used by End-Users or Domain Experts.
Using the optional Quaestor project file DataBase, project files can be saved in the project database. In this way you can query in all data of projects saved in the database and use the results as data in your (new) project.