The program is CLIT 1.8. You can get it by doing a Google search. CLIT.exe is the name. You can use it to convert to HTML or just breaking the DRM. You have a few choices. If you convert to HTML you can use html2lrf to convert to LRF or if you ust remove the DRM you can use lit2lrf to convert to LRF or finally load the LIT into Book designer and work with it from there.
html2lrf and lit2lrf are part of the libprs500 package.
html2lrf -
https://www.mobileread.com/forums/showthread.php?t=10582
lit2lrf -
https://www.mobileread.com/forums/showthread.php?t=11618
Book Designer and the current update
https://www.mobileread.com/forums/showthread.php?t=11786