Various tablature formats can be sometimes converted or translated to be of use in a different program. So it may as well be possible to convert Power Tab files (.pb) a one of the Guitar Pro formats, including .g5 files from version 5.
Convert Power Tab guitar tablature editor file to Guitar Pro 5 project.
We have found one software suitable in our database for this conversion.
Linux/Unix software - convert ptb to gp5 on Linux
Open source tablature editor and player
Convert from ptb file format
The table with program actions contains information about what each program is capable of doing with their files. This may be a good pointer for further searches for certain file conversions and help you find the converter you are looking for if our search result is insufficient for you. However, it is far from perfect and may sometimes show results which are not really usable because of the nature of the software handles the files. So a conversion that appears as possible, just because of matched actions, may in fact not be possible.