Google Drive Documents can be embedded directly using the Google Sites.
You can embed Google Drive Documents documents like Spreadsheets, Charts, Diagrams, Drawings, Presentations, Forms and many more.
Syncronize Google Drive Documents with a Google Chrome Extension.
Other documents such as pdf files and Third party formats can be placed in a <iFrame> tag. Flash SWF animation can be placed in a Object tag.
Some Embed examples for Google Sites and Third Party Embed Examples.
Google Sites Examples - Embed