Hi Ian
It rather depends on what the third party software is, and the kind of data you are interfacing with it. HansaWorld's software has export and import formats for all registers, as can be found from the report Export/Import Format in the Technics module.
However some of these formats are long, e.g. the Contacts register has well over 200 fields, many of which won't be used in your system, so the other method is to take the file format from the third party software and customise the HansaWorld software to export and import in this format. This would be chargeable programming, and would require you to have the HAL licence, but in the long run it may be easier than having to manually manipulate the data each time.
Regards
Paul Timms
IT System Integrators