How to get the html content from another page ?

Hy,
 
I am using the <customErrors mode="On"  defaultRedirect="webforms/wFrmErro.aspx"  /> in the web.config to redirect the page erros. I need to send an email with the exception message and the html content that generated the error. Right now I am already sending the email with the exception message but I didn´t figure out yet how to get the html content. I already tryied to use the HttpContext.Current but I didn´t see any properties or methods to directly get this content. How can I do this ?

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