I'm wondering if it's possible to retrieve a simple GoogleDoc (via gdata python client) and render a PDF replacing some custom #[PLACE_HOLDERS] with my own information.
Found what I've looking for. The problem was that I tried to use DocsService (v1 API) instead of DocsClient (v2).
WARNING: The examples of gdata/OAuth in AppEngine are outdated - http://code.google.com/p/gdata-python-client/source/browse/samples/oauth/oauth_on_appengine/main_hmac.py.
To get an updated version check this link (It's for Django, but you only have to change the request/response) - http://pamelafox-samplecode.googlecode.com/svn/trunk/spreadsheetsimporter/importer/views.py
So after changing the Oauth method to a newer version, I managed to get the file contents in HTML,DOC,PDF, TXT, etc. Just change the exportFormat.
For the future, if anyone needs:
_client = gdata.docs.client.DocsClient('My-Prety-App-v1')
# Set your prefered auth method
# ...
entry = _client.GetDoc('document:XXXXXXXXXXXXXXXXXXXXXXXXXXXXXX')
exportFormat = 'html'
content = _client.GetFileContent(uri=entry.content.src + '&exportFormat=' + exportFormat)
self.response.out.write(content)