Gets the parameters associated with the OpAtom at the specified
index and validates that the atoms are of the correct type.
Because the arguments are validated and the types are checked so
you can rely on the fact that the returned array contains a valid
number of Atoms of the correct types.
Only the top level atoms are checked. So for example, the TJ
operator takes an ArrayAtom consisting of NumAtoms and StringAtoms.
This function will ensure that there is one ArrayAtom available as
a parameter. However it will not ensure that all items inside the
array are NumAtoms or StringAtoms. Also resource lookups are not
done so, for example, it is not checked that a font name actually
exists in the font resource dictionary.
If the operator takes no parameters a zero length array will be
returned. If the operator parameters are incorrect or if the
operator is not recognized then the return value will be null. In
this unusual situation you may wish to set the OpAtom.Text to white space to remove
the invalid operator from the content stream. While this does not
fix the underlying problem, it will at least prevent applications
like Acrobat from reporting an error.