Custom agent and setContentType

Hi...

I don't know if this is a FAQ, but... I'm trying to send a PDF file to the browser, using a custom service. 
In it's service() method, I set the contentType to "application/x-pdf", but Internet Explorer insists in ask the user if the file must be opened or saved. I think IE is ignoring the Content Type header. 
I'm doing something wrong or there is some known trick to do this work? I can send the service class I did, if it helps.

Thanks

    Robson