Unable to display SharePoint pages from a different domain in iFrame
Original KB number: 4531668
An error occurs when loading SharePoint pages inside an iFrame that originate in a different domain.
This is by design. Loading pages in this manner will not work because the HTTP header property
X-FRAME-OPTIONS is set to the value SAMEORIGIN.
Overriding this property by setting the web part to AllowFraming isn't recommended for security reasons. There are several functionalities that will not operate correctly when loaded into iFrame. (This behavior will vary from browser to browser.)