LRF file - The digital book format originally used by Sony Corporation. It is a proprietary format, but some reader software for general-purpose computers, particularly under Linux - with index of search terms.
After purchase is completed, you will receive an email with the PDB file attached. Be sure to check your spam/junk folders if the email doesn't appear in your inbox. Save the attachment (or click the Download link on the Document order details form) to your computer. Then connect your device to the computer using the provided USB cable, and copy the file to the documents folder on the reader.