Kathleensmum, does the pdf come through and open ok on the iPad if you send it via email and open it via email on the iPad? If it does, one thing your ds could try is to open it in another iPad app, and then send it to his teacher via email from the second app. It's extra steps to go through, so not a great solution, but it would at least help determine if the issue is the file Panther is outputting or an email translation issue on the pc side related to iPad -> PC.
I'd suggest trying to email Panther and ask if they have any idea what's up.
And... not sure if your school folks can figure this out, but another thing to consider is to allow your ds to print via the network at school - he could open the pdf on his iPad and send to a printer. It's not always easy to get school staff to help with printing (successfully) though - at least not in our experience. Never really had it working just from a laptop at ds' previous school, but at his current school the kids print from their iPads and ds used to print from his iPad at home across our wifi network too. Although to be honest, I have no idea how to set it up! (ps - ds said you can get an iPad-usb adapter to hook up directly to a printer).
Good luck,
polarbear
