Hey Mike,
Thanks for reaching out with your BoldGrid Post and Page Builder questions! I’m not sure if you can add an iframe directly to a button in your page editor but you should be able to add it directly to the page itself. If you’re inside of your Post and Page Builder editor. Just above the design area you’ll see a “Visual” and “Text” tab to the right.
If you click the text tab it will allow you to add HTML directly to the page. You can add your iframe to the text area in any place you would like it to display. You can also switch back to the “Visual Editor” at this point, to move the iframe around on the page. Publish or Update your changes and check the live site to make sure the iframe displays properly.
I hope this helps Mike. Let us know if you have any other questions for us!