Conversion PDF -> Epub

[rudmueller]

Hello everybody,

I have been trying to convert a PDF document (Photomatix Pro 4 manual) into the Epub format. Calibre doesn't recognize the punctuation dot (full stop/period) and replaces it by a question mark in a black square put on one of its corners. Dotted lines become lines of question marks, the same thing shows up at the end of each sentence.
Is there a possibility of avoiding this mistake respectively of restoring the correct sign?

Thanks for answering
Best regards
rudmueller

PS: This is the 1st and only time that this eroor has appeared.