Supposedly the less known POP format from Samsung Popcon is supported in Adobe Photoshop, probably with some plugin. So it would be your best option to try it if you want to use it for making gradients.
Convert Samsung Popcon animation to Adobe Photoshop gradient preset.
We have found 2 software records in our database eligible for .pop to .grd file format conversion.
Microsoft Windows software - convert pop to grd on Windows
One of the best bitmap graphic editing program
Convert from pop file format
The tables with software actions are a good pointer for what a certain program does with various file types and often may give users a good hint how to perform certain file conversion, for example the above-mentioned pop to grd. However, it is not perfect and sometimes can show results which are not really usable because of how certain programs work with files and the possible conversion is thus actually not possible at all.
Apple macOS / Mac OS X software - convert pop to grd on OS X
Mac version of popular digital image editor