Sorry
Mike - just assumed that the attachment was a photo; if a multiple page PDF file and as you likely have already done, the file can be opened in the mail app, but I'm not aware that a rotation is possible; of course, the file can be exported to other apps on the iPad, such as iBooks & Goodreader, but not sure if there is an option in those programs to do an inversion? Hopefully, others may have suggestions for an app w/ that capability.
BTW, if you use the other excellent suggestion made, keep in mind that the side switch is defaulted to 'mute' the sound, but can be re-set to 'screen lock' in the 'Settings' app or the multi-taskbar can be opened and the screen locked from the far left (i.e. swipe right); however, if you find a solution, please post back - might help others. Good luck -