Simply follow the instructions that come up when you do a search on Mac-Forums.com for "pdf default" or "adobe reader default"
Just curious, why do you want Adobe Reader over Preview?
Right click on a PDF File and click on Get Info. Then go down to Open With and change to Adobe Reader. Then under that a button called Change All will un-Gray. Click that. All PDFs should open in Adobe after that.
Edit: I am grabbing it now. If what I told you does not work, let me know. I am going to try it.
Tried it, works. Everything PDF opens in Adobe Reader.
I have never had any issues with Preview so far.