[HarryT]

CoolReader is a seriously broken ePub reader and displays innumerable books either wrongly or not at all that are absolutely fine in other ePub apps. I'd suggest using a different reading app.

Having said that, however, PDF is of course the worst possible format to convert from, and PDF conversions will generally be riddled with errors, so in this specific case it's entirely possible that the problem lies with the book. I'd suggest looking at the book in Calibre's editor and seeing if it really does have line breaks where the app is showing them.