We cannot embed iframe in a visual workflow. We can, however, include a visual workflow and an iframe in a visualforce page. Here is an example: https://developer.salesforce.com/blogs/developer-relations/2011/10/dynamic-visualforce-and-visual-workflow-with-rerender.html
If this answers your question, please mark this as the Best Answer for this post, so that others can benefit from this post.
We cannot embed iframe in a visual workflow. We can, however, include a visual workflow and an iframe in a visualforce page. Here is an example: https://developer.salesforce.com/blogs/developer-relations/2011/10/dynamic-visualforce-and-visual-workflow-with-rerender.html
If this answers your question, please mark this as the Best Answer for this post, so that others can benefit from this post.
Thanks,
Shashank