Packet Tracer seems to be capable of saving data from *.pkt files (network simulation) and export it as activity files (*.pka). We haven't found any other 3rd party software capable of PKT to PKA conversion.
Convert Packet Tracer network simulation file to Packet Tracer practice activity file.
We found one software available in the database for this conversion.
Microsoft Windows software - convert pkt to pka on Windows
An interactive teaching and learning tool
Convert from pkt 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.