.PBXPROJ File

File extension pbxproj is related to Apple Project Builder and used for projects created and saved in it. Older format, but still can be opened in Xcode.

Files with pbxproj suffix might mostly found as projects from Apple Project Builder program.

How to open:

As a successor to Project Builder, Xcode can directly read Project Builder projects.

How to convert:

A conversion is unlikely, but projects can often be exported.