How can I open an mpp flie? How can I convert it to an ordinary file type so that I can open it?

Mpp is Microsoft project plan, it is used with the Microsoft project software. I don't think you can convert it to be used in anythign else, other than opening it in Microsoft project and maybe saving it as some other format (but I've never used Microsoft project, so I don't know that this would work either).

Hopefully this is a helpful start and someone with knowledge of Microsoft project can help further.

Capuchin is correct, that is a MS Project extension that can only be opened by MS Project. Once you have it opened you can save data in an Excel sheet or as a jpg table or graph.

You can purchase a viewer for Project files here:

Microsoft Project Viewer for the PC, Mac, and Linux (http://www.steelray.com/spvmpp.html)