AZW and AZW3 files are ebooks from Amazon Kindle with the latter being the successor of the original format. Both formats often use DRM protection so it is not that easy to convert them, but for ebooks without any DRM, it should not be hard to repack them to newer format with ebook converter that supports that kind of thing.
Some users circument this by exporting .awz files to PDF/EPUB and converting that to .azw3, but that only works by removing the DRM, which is questionable.