1. Open the document from Google.
2. Click File (green).
3. Click publish to the web (orange)
4. Click Embed (blue underline).
5. Click on Publish (orange).
6. Press ctrl+c to copy the code.
You can resize the dimensions for your embedded document by inserting the pixel size you require. Just Edit the code item and copy/paste the code below including your URL and changing the pixels as required.
<iframe width="400px" height="400px" src="YOURDOCUMENTSOURCEURL"></iframe>
Enter the width and height code directly after "