A flash file can be embedded in a PDF document. Does anyone know if it is also possible to embed an HTML webpage?
Added:
Not directly. Depending on what you're looking for, however, you can use something like dompdf (PHP) to generate a PDF file from an HTML document, then merge that document with your original. It even supports JavaScript, up to the level Adobe Reader supports JavaScript.
That said, the PDF file format is really for things you want to print (i.e. want to look the same everywhere), not things you want to click on (i.e. look sensible everywhere). Adobe's decision to include Flash support was probably made from a marketing standpoint, not a technical one.