You can define any HTML elements in the form view inside a div. For example:

<form string="Vehicle">
    <div><iframe height="500" width="500" src="http://google.com"></iframe></div>
</form>

Also, You can apply JS 

The answer is done after testing the code. Don't downvote for fame. The answer will be helpful to others.

This the screenshot of the output. Inside the notebook -> page element, I simply defined as above. But the link is odoo.com

The screenshot of external page inside the sheet directly,

Hi,

Set form view type as html

<field name="arch" type="html"/>

in arch body you can define iframe tag to load any url as external page.

i hope this will give you an idea to implement.

Regards

Haresh Kansara