Downloaded from Mail .pdfs being renamed

I noticed that some .pdfs I'm downloading in the mail from a client with some specific names to help me determine when I post them in iWeb whether it's the password-protected .pdf or the non-password protected .pdf are being renamed using the client's email name and numbers instead of the name he sent them. I see the correct item in the mail, but after it's downloaded it is a completely different name. How can I stop that?