The flashplayer can only launch the browser by design.
If you want to open a file that runs outside of the browser, you will need to use the fscommand method.
in a new text file, write a line similar to the following:
save the text file as "launcher.bat"
put this bat file in a folder next to your flash executable called "fscommand" - also place the pdf in that folder.
In the flash:
fscommand("exec","launcher.bat"); //this launches the batch file, which launches the PDF. This method can be used for any type of file.