So here's something stupid that I just recently figured out how to do, I replaced the thumbnail of _paint.net project files. If you are curious on how I managed to do that, I have (currently incomplete) documentation on how the format works over on GitHub. github.com/TheAstralSno...
.pdn
A repository focused on collecting as much knowledge as possible on as many image file formats as possible. - TheAstralSnowstorm/Image-File-Format-Knowledgebase
github.com