The problem with character "?" (pdf->epub)

I would be grateful for assistance of advabced User!:help:

I try to convert some text from pdf-file to epub-file by means of Calibre. And I want to remove all page headers in epub-file after the conversion.
The problem is that the built-in Master of replacement doesn't want to find any regular expression, containing character "?", in pdf-text. So I can not remove symbol "?" from all page headers, containing it.
The Master of replacement easily removes the text of any page header, but the character "?" - if it is - always is left in epub-document after the conversion.
Why?
How can I kill off this character in output epub-text?

Thanks in advance!