Originally Posted by DiapDealer
If you have an ePub—use the ePub.
Yes, absolutely. The title of this thread says "converting ePub to Mobi". If you are indeed converting an ePub file to Mobi, you don't need to worry about the OPF - just use the ePub file as input. The only time you need to worry about the OPF is when (as I do) you're creating the Mobi from "scratch", rather than converting from an already existing ePub.