There are many kinds of pdf files. Some have basic formatting, some are really very very complicated. So, there is not one recipe but many solutions.
My try first would be to try to read it straight away, my second to try a calibre convert.
If these two fail and you desperately need the book, you'll have to dirty your hands.
- a multi-column text can be processed with Fine Reader as a rtf, then even text
- a one-column with Acrobat with text and images saved separately and mixed later
As some people told you already on this thread, working with text can solve everything except hours of work...
