Both the .ltz and .hdz files are used by Poser 3D modeling software. It is not clear whenever both of these files can be converted from one to another and vice verse, however it seems to be unlikely. At best, you could apply data / settings from one file to another when you create or edit a model.
Convert Poser compressed light set file to Poser compressed hand pose file.
We found one software available in the database for this conversion.
Microsoft Windows software - convert ltz to hdz on Windows
Program for making 3D character arts and animations
Convert from ltz 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.