How to use beautiful soup to parse this xml file?

I am trying to use Beautiful Soup to parse xml files, I tried reading the documentation of BS at Crummy but could not find anything satisfying for xml parsing. Right now, I've been able to figure only this much out:

file = open("input.xml")
page = file.read()

soup = BeautifulSoup(page, "xml")
for word in soup.findAll('word'):
    word_attr = dict(word.attrs)
    netag = word.find('ner')
    nertag = dict(netag)
    print ("STOP", nertag['ner'])

But, it is not doing anything. My xml file is of the form:

<?xml version="1.0" encoding="utf-8"?>
<root>
 <document>
  <sentences>
   <sentence id="1">
    <tokens>
     <token id="1">
      <word>
       Starbucks
      </word>
      <lemma>
       Starbucks
      </lemma>
      <CharacterOffsetBegin>
       0
      </CharacterOffsetBegin>
      <CharacterOffsetEnd>
       9
      </CharacterOffsetEnd>
      <POS>
       NNP
      </POS>
      <NER>
       ORGANIZATION
      </NER>
     </token>
     <token id="2">
      <word>
       to
      </word>
      <lemma>
       to
      </lemma>
      <CharacterOffsetBegin>
       10
      </CharacterOffsetBegin>
      <CharacterOffsetEnd>
       12
      </CharacterOffsetEnd>
      <POS>
       TO
      </POS>
      <NER>
       O
      </NER>
     </token>
<token id="5">
  <word>
   .
  </word>
  <lemma>
   .
  </lemma>
  <CharacterOffsetBegin>
   263
  </CharacterOffsetBegin>
  <CharacterOffsetEnd>
   264
  </CharacterOffsetEnd>
  <POS>
   .
  </POS>
  <NER>
   O
  </NER>
 </token>
 </tokens>
   </sentence>
  </sentences>
 </document>
</root>

What I am trying to do is to extract the NER values, remove the period punctuation with "STOP", and write this to another txt file.

Like for a sentence: Starbucks in New York is good. (Written in an xml) Should give: ORGANIZATION in LOCATION is good STOP

Can somebody please help me how to do this? Or provide me with sufficient documentation for Beautiful Soup xml parsing?