I don’t know what a .webp file is but I don’t like it. They’re like a filthy prank version of the image/gif you’re looking for. They make you jump through all these hoops to find the original versions of the files that you can actually do anything with.
Image file format with excellent compression. It’s designed for web browsers, so what you’re probably running into is compatibility with other programs. It’s fairly easy to convert though to GIF or JPEG formats though.