Preview IS the default app to open pdf files. Right click on the pdf document > Get Info > Open with: > choose your app or Other if it isn't listed, navigate to the app in Applications > Change All.
Thanks -- usually that works but its not finding Adobe to open it but I know I have it so if I could change the default it would automatically use it.
I have searched all over the internet and the suggested fixes are like reading War and Peace. This is one thing I find annoying with Apple. There ought to be a simple way to do this but I guess there isn't.
Well then, you either have not installed it correctly or you have installed it somewhere other than the Applications directory.
If you would take the time to learn Mac OS X with an open mind then you'd find that it's pretty easy to do things with an Apple computer.
What apps are listed when you right click on the PDF file > Open With?
Is Adobe Reader listed in your Mac Application directory?
If it is, is it greyed out when you click on the "Other" button?