Originally Posted by david1150
Have you tried Calibre? It allows you to convert .mobi files to .rb files. It also accepts just about any input format and translates it into anything else. I don't see .imp on the list, but this may be one of the few exceptions. Go to http://calibre-ebook.com/
and download it for free.
A caveat on this comment. Yes, about any book-format (newer) may be translated into .rb but the line-length and spacing lacks control. And the eBookwise Librarian will convert .rb books into .imp format. But the line height may be too small to allow you to read the resulting document.
On the other hand, if you convert to .rtf format or a text format, you may drop the resulting file into an HTML editor or use GNU-Emacs to manually add HTML markings. And add a <style> section to set the line-height to a valid size. Then eBookwise Librarian will produce satisfactory output, readable and crisp.
I asked Kovid Goyal about the .imp format and inclusion into Calibre. No plans exist for adding the format. He implied that he is not interested in adding the format at any future time, either.
So often ereaders seem to be set to only use the "modern" formats and neglect the many books already out in older formats. That's one reason why I keep a Pocket PC around with readers for .lit, .pdb, and .mobi/.prc books. Especially since line spacing and looks often suffer a beating or require a major edit before conversion.