PDFs are notoriously difficult to convert to other formats. The Book Designer program preserves the formatting of the PDF well but, as mentioned above, there may be characters that cannot be converted. When I feed Book Designer PDF files, I sometimes get question mark characters instead of letters in the middle of a word.
I agree with Liviu_5 above that your best option is to convert the PDF to a text file (giving up italics and bold text) and then convert to IMP. Instead of using the Adobe reader to do the converting, I prefer the "Free PDF Text Reader" available here:
http://www.ctdeveloping.com/ctdevelo...eader_info.asp
This program preserves the layout of the PDF better than Adobe.