Your question isn't very clear.
You're developing a windows forms application ? WPF application ? or ASP.NET web application ?
So you're getting some html string as input and you wish to show that HTML as web-page inside an iframe tag. Right ?
InnerHTML won't work for iFrame as html between opening and closing iFrame is parsed only if iFrame is not supported.
You'll have to create a temporary html file from that string and give its path to iFrame's src attribute.
Need to know which kind of application you are making.
Thanks
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