The SurPad 4.2 software supports the following geoid file formats for import: *GGF, *SGF, *UGF, *GSF, *GRD, *GTX, *BIN, and *XYZ. I will be sharing Geoid files for Australia here as soon as they become available.
The files include:
2. AUSGeoid2020_20170908_win.sgf