Is there anything else on the page/assignment besides the embedded document?
If this is something on it's own, with no additional content, the easiest solution might be to just delete the entire page/assignment. However, if you have other content then it could depend on how you embedded it. For example, if embedded into an assignment as an External Tool submission, then you would go into the settings at the bottom of the assignment editor and just remove the External Tool option. If embedded using the Document menu option in the editing ribbon, it usually defaults to a link that, when clicked, expands the preview. That just requires removing the link in the editor. If you used an iframe because you got embed code from another site, then that is something that sometimes is more easily removed through the HTML editor. You can sometimes put the cursor (in the editor) in front of or after the content, then use Delete/Backspace to remove it as well.
These are the more common ways I see stuff embedded. If you used a different method, please describe what you did.
