I have not found a decent PDF->ePub converter. But a couple of points:
(1) You may have to do considerable hand-editing to get the format straight. Sigil can be very useful for this.
(2) Some of the "junk" characters may not be actual junk but instead special characters. E.g., ligatures such as "fi" may appear in a text editor as bizarre symbols, but will render just fine in an ePub viewer. Of course if they also appear as junk in an ePub viewer, you have a different problem...
|