TOPO! navigation software should generally support import of files saved in GPX Exchange format (.gpx) and use the data for making .tp mapXchange documents. Probably the easiest and most likely also only program capable to perform this gpx to top conversion.
Convert GPS eXchange format to TOPO! mapXchange document.
We have found one software suitable in our database for this conversion.
Multiplatform software - convert gpx to tpo on any platform
A topographic mapping software from National Geographic Maps
Convert from gpx 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.