If you want to embed the content of a Google Doc, slide deck, or sheet, you can use the embed menu in the editor. Just click the 'Embed' option and paste the link to your Google asset.
Only users who are logged in to their Google accounts with access to the asset will be able to view the content.
How to Minimize Google UI
If you just need to view the content of a doc or sheet, you can add ?rm=minimal to a Google Sheets/Docs iFrame to remove all the menu items.
Adding an External Link
If you'd like to add a Google asset to your knowledge base without embedding it within a page, check out how to create an External Link here.