I use the internet explorer activex control. This way you can display it inside a form if you wish. Also, if you set it up properly, you can view any file that IE will open, not just PDF's. I use it for DWG's, PDF's etc...

But the client machine must have the IE plug-in associated with the file type.

For instance, when someone installs adobe reader, it automatically installs a plug-in for IE that will cause all PDF's on the web to be opened by IE.

Just remember to put "nodefault" in the activex refresh event. (bug fix)