Nate Yiu

For what it's worth, I didn't use recursion for my solution precisely because it mentioned the trees are large.

@JorjMcKie I see. So in examples like this where I want to make sure the user passed in a PDF, you would advise checking the `doc.is_pdf` flag, correct??

Yes, please go ahead. And thank you for the quick and helpful reply. I will leave the issue for you to do as you wish.