Now to the individual tasks, that will be put to you via the callback being indicated by various values of scLlDesignerPrintJob._nFunction. The symbolic constants for them all start with LL_DESIGNERPRINTCALLBACK...:
Start Event (..._PREVIEW_START/..._EXPORT_START)
Abort Event (..._PREVIEW_ABORT/..._EXPORT_ABORT)
Finalize Event (..._PREVIEW_FINALIZE/..._EXPORT_FINALIZE)
Status Query Event (..._PREVIEW_QUEST_JOBSTATE/..._EXPORT_ QUEST_JOBSTATE)