I have a 4.0.x binary installation of alfresco and have this menu highlighted below:
I have 2 custom installed 4.2.c versions and this option is missing. I have done the following to try and enable it as read from different parts of the web:
1) added the two following lines to both the share and the repo's alfresco-global.properties file
#enable GoogleDocs integration
googledocs.enabled=true
googledocs.googleeditable.enabled=true
2)Modified the share-custom-config.xml file in attempts to enable this and other google docs functionality.
So far this is the only thing missing. I am not sure whether this is a bug or whether I'm overlooking something else.