You may need to clarify you question above - first, I'm assuming that you mean the 'display' on the iPad screen? This can be captured as a JPEG photo and stored in the camera roll of the Photo App (done by simulataneously pressing the On-Off & Home buttons) - now I'm assuming that you would like to convert that into a PDF file?
Well, if possible the process would require some 3rd party app - just gave Goodreader a try on my iPad w/o success; hopefully, others may 'chime in' w/ suggestions or apologies, if not possible.