Creating PDF out of iFrame

Hi, I have iFrame implemented on my page.
When I try to use SelectPDF it returns the initial picture of this.
I was trying to workaround it with 3rd party services which produce PDF out of html (reference below). But I cannot figure out how to extract HTML source from the page.
Is there maybe some other way how to handle it?

Many thanks for any ideas!

Did you find a way to do this? Please can you share if you did?