Remove default from pdf route

app/flaskr.py

@@ -19,7 +19,7 @@ def index():
     return send_from_directory('static', 'index.html')
 
 
-@app.route("/tutorial/<document>.pdf", defaults={"document": "book"})
+@app.route("/tutorial/<document>.pdf")
 def tutorial_document(document):
     """Display tutorial document"""
     return send_from_directory('static', 'tutorial/%s.pdf' % document)