Use Case:
I would like to use RS Documents to print labels onto envelopes. How can I set this process up?

By default Google Docs doesn’t seem to have a page setup option for envelopes.  We would suggest looking at an add-on like this one to see if possible to setup the template:  We have not tested this ourself so you would need to see how it looks and if it would work. If not maybe could try to get the formatting to work for envelope print using google doc.  Also can maybe consider exporting to word?