Linking pb file to the Qt program.

[anda_skoa]

The third code only works when I ran my program inside my machine and I understand that since it is the absolute directory of my pb file.

Yes, correct.

And the first two are relative paths, the program will look for these in the current working directory.
The current working directory is very often not the program's installation location.

As ChristianErlicher wrote, you can create a path relative to the executable.

Even adding the pb file to the resource didn't solve.

Well, not if you pass the resource path to a non-Qt library, it won't understand this type of path.
For this kind of usage the resource data needs to be first extracted into a real file, e.g. using QTemporaryFile::createNativeFile().

Cheers,
_