MIME type and pdfs

[warpdrive]

I have a problem with my Plesk server. I have two sites with pdf downloads. However when I want to view them in the browser it automatically wants to download the files. I want the browser plug-in to view them but it fails to do that. I imagine it has something to do with MIME.type file. I have checked this but it has the pdf components there so I can't figure out why all the browsers I try want to download the file.
I have tested this in IE/Firefox on a PC and Safari/Firefox on a mac and all seem to do the same thing.
Can someone help.
Thanks