An AZW3F file is a metadata file used by Amazon Kindle, an e-reader device. It contains metadata, such as the author and number of pages, for an .AZW3 eBook file, which is an Amazon KF8 eBook format that replaced the .AZW file format.
Since AZW3F files store metadata for AZW3 files, they typically are stored in the same directory. AZW3F files are typically located in the .sdr directory on the Kindle. Therefore, if you come across an AZW3F file, there most likely is an AZW3 file nearby. However, even though AZW3 files are meant to be opened, you should not open AZW3F files.
Common AZW3F Filenames
[same name as AZW3 file].azw3f - AZW3F files bear the same name as the AZW3 file for which they store metadata.