input: Write a python function to count words in a PDF document.
  assert count_words("This is a sample PDF with seven words.") == 7
  assert count_words("Another PDF document with exactly nine words in it.") == 9
  assert count_words("PDF with only three words.") == 3
output: def count_words(pdf_text):
      words = pdf_text.split()
      return len(words)