It depends what you wish or think the users will do with the output. if its a:
- certificate I would produce a PDF for sure. You need a guarantee it hold form/style etc...
- Invoice I would just make sure its not editable, so PDF or HTML. Not word.
but is this the accepted norm to generate a new page/tab as a HTML-generated report?
of course, why not. As I said above it depends what you wish or think the users will do with the output