This widget embeds an iframe and also provides a link for devices that don't support iFrames. Document will display in "preview" mode, but the link can be set to open in preview (default), edit, or copy mode.
Using this widget
{{#widget:GoogleDoc
|key=1pj6gRX6dnA0B8WZams5tumAVMdCyMoUNIxP5LZeA9AA
|mode=copy/preview/edit
|width=800
|height=400}}