LRF, Sony Portable Reader File (.lrf)
The LRF eBook file format
Sony brand eBook eReaders (such as Sony Librie and Sony PRS-500 readers) utilize the LRF file extension for their documents and texts. This proprietary file type is now obsolete, as well as the related LRS and LRX files. Those three file types made up the BroadBand eBook (BBeB) which was discontinued in 2010 when Sony began selling their ebooks in the EPUB format (which is more versatile and can be used on most devices with eReader capabilities). This allowed for more books to be purchased and downloaded with less conversion.
Technical details of LRF files
LRF files are XML files that can be edited. They followed along the BBeB Xylog XML specifications, representing the source code for the BBeB eBooks. While LRS files are open source, LRF and LRX files are not. Special tools allow conversion between LRS and LRF using the XylogParser.dll which is available to everyone though. LRF files can contain both text and images, much like other eBooks. Information about the LRF files and family is difficult to obtain due to the lack of documentation for the LRF and related files.