Hello
Is it possible to make sure that the urls of the iframe contents are also converted?
In my case I have an iframe that contains a flipbook and apparently the url remains that of my hosting, not to cloudfront.
Could the cause be the fact that I excluded js and css from the CDN?

Yes, you're right. I should try to figure out if the images (jpg) in the flipbook are uploaded from cloudfront or not, but it is hard to tell in the js code.