.kra is Krita’s internal file-format, which means that it is the file format that saves all of the features Krita can handle. It’s construction is vaguely based on the open document standard, which means that you can rename your
.kra file to a
.zip file and open it up to look at the insides.
It is a format that you can expect to get very heavy, and isn’t meant for sharing on the internet.