We do not know about any useful purpose for png to nd2 conversion, although it is theoretically doable, purely because both files are raster graphics.
ND2 format comes from a range of digital microscopes from Nikon and is digital RAW format recorded for a very specific purpose and further analysis. If you convert random picture to this (even previously exported .nd2 file) it will lack all the necessary meta data and variety of parameters recorded during the capture.
All this means that whilst you probably can find graphic editor that can convert png to nd2, it's pretty much pointless conversion.
Updated: October 12, 2023