My friend is using an iMac, don't know which one, but he is still running Tiger Intel. He uses Hot Mail for his email service which is either on Foxfire or Safari. When I send him a PDF from my Mt. Lion Mac Mini, he gets a "warning" notice and can not open the email. Apparently, this only happens when I send a PDF file or my husband sends a PDF from Snow Leopard mac mini. I and my husband use Firefox. BTW. when I send him a simple email, he has no problem. Can anyone tell me what might cause this? I have my guesses, but would like to consider someone else's guesses. Thanks for reading my crazy question.