|Is it OK to use Oracle documentation to answers questions?
||Yes! The main objective of the PL/SQL Challenge is to improve your knowledge of the PL/SQL language. Very few developers will know enough about PL/SQL and the various packages that help make it a robust language to figure out the correct answer without resorting to documentation, whether Oracle's or another's (such as Steven Feuerstein's books).
The scoring algorithm ensures that people who are able to answer without looking up information will score higher, because it will take them less time to answer. Remember, though, that the scores emphasize correctness over time.
Thus, the more familiar you become with more of PL/SQL, the higher you will score over time.
So by all means, study and research to your heart's content!