PDTextSelectEnumTextUCS() function failing to extract special characters like ≤ ≥ Ω ∞ ≠

PDTextSelectEnumTextUCS() function failing to extract special characters like  ≤  ≥  Ω ∞ ≠       I am using the callback function PDTextSelectEnumTextUCS(), there I am trying find the text items, which may contain the characters like ≤   ≥  ...  but failing, how to extract correct text for the same.
The normal text it is fetching correctly.