Page Previews Beautiful - Saved Copy Not So Much

I acquired an epub book that I am pretty sure was originally a pdf. When I open the .epub it is pretty crappy: bad formatting, tiny font, etc. If I open it in the editor it looks much much better in the file preview of each chapter. If I "Save a Copy" it looks like the input (crappy).

I rarely use the editor so not sure how to output an .epub that looks as pretty as the file previews of each of the chapters in the editor???