Odoo Server Error

Traceback (most recent call last):
  File "/home/salvatore/seedoo/OCB/openerp/http.py", line 546, in _handle_exception
    return super(JsonRequest, self)._handle_exception(exception)
  File "/home/salvatore/seedoo/OCB/openerp/http.py", line 583, in dispatch
    result = self._call_function(**self.params)
  File "/home/salvatore/seedoo/OCB/openerp/http.py", line 319, in _call_function
    return checked_call(self.db, *args, **kwargs)
  File "/home/salvatore/seedoo/OCB/openerp/service/model.py", line 118, in wrapper
    return f(dbname, *args, **kwargs)
  File "/home/salvatore/seedoo/OCB/openerp/http.py", line 316, in checked_call
    return self.endpoint(*a, **kw)
  File "/home/salvatore/seedoo/OCB/openerp/http.py", line 812, in __call__
    return self.method(*args, **kw)
  File "/home/salvatore/seedoo/OCB/openerp/http.py", line 412, in response_wrap
    response = f(*args, **kw)
  File "/home/salvatore/seedoo/OCB/addons/web/controllers/main.py", line 948, in call_button
    action = self._call_kw(model, method, args, {})
  File "/home/salvatore/seedoo/OCB/addons/web/controllers/main.py", line 936, in _call_kw
    return getattr(request.registry.get(model), method)(request.cr, request.uid, *args, **kwargs)
  File "/home/salvatore/seedoo/OCB/openerp/api.py", line 268, in wrapper
    return old_api(self, *args, **kwargs)
  File "/home/salvatore/seedoo/seedoo-core/seedoo_protocollo/wizard/create_protocollo_mailpec_wizard.py", line 353, in action_save
    body_pdf_content = base64.b64encode(ConversionUtility.html_to_pdf(wizard.body))
  File "/home/salvatore/seedoo/seedoo-core/seedoo_protocollo/wizard/utility/conversion.py", line 38, in html_to_pdf
    tempfile = ConversionUtility.html_to_pdf_file(body=body, css_file=css_file)
  File "/home/salvatore/seedoo/seedoo-core/seedoo_protocollo/wizard/utility/conversion.py", line 32, in html_to_pdf_file
    extra_args=extra_args)
  File "/home/salvatore/seedoo/venv/local/lib/python2.7/site-packages/pypandoc/__init__.py", line 69, in convert
    outputfile=outputfile, filters=filters)
  File "/home/salvatore/seedoo/venv/local/lib/python2.7/site-packages/pypandoc/__init__.py", line 325, in _convert_input
    'Pandoc died with exitcode "%s" during conversion: %s' % (p.returncode, stderr)
RuntimeError: Pandoc died with exitcode "41" during conversion: pandoc: wkhtmltopdf not found. wkhtmltopdf is needed for pdf output.