P3 - Primavera P3 Project File is mainly used for Primavera P3, which is a scheduling file. It is used for planning software and construction projects. You will be able to use this wonderful extension to save tasks, timelines, and come up with different resources. You can use this extension when allowing the project manager to plan and track the progress. You will still be able to open up all of your P3 projects in Primavera p6. All you will have to do is simply choose the file and import from application menu. It is very simple and easy to use.