It is possible to convert from PDF to LRF (or most of the other e-book formats) in one step using free program "Book Designer". It can be downloaded from
http://www.the-ebook.org/rus/?cat=21, download links are at the bottom of the page on the left (the site is mostly in Russian). You will need "BookDesigner v.4 Installer" and "BookDesigner v.4 обновление программы". After running the installer copy files from the second archive on top of the installed files, which upgrades version to 5.0. The help and instructions are in English.
The program works on almost every PDF file I've got my hands on. The conversion is not perfect, e.g. with some files footers got mixed into the main text, but in most cases the result is quite usable.
I am not author of the program but I've used it a lot and can answer some questions.
Best regards,
Alex.