I installed Chrome 17.0.963.56 on my MAC running MAC OS 10.6.8. I cannot find where to make the Adobe Reader the default in the preferences.
As you asked 'In Chrome':
You just need to type 'chrome://plugins' into the address bar. Scroll down to search for 'Chrome PDF Viewer' > Click the disable link just below it. Following the 'Chrome PDF Viewer', next would be 'Adobe Reader' and simply click Enable.
P.S- As per my experience, the 'Adobe reader' plugin is way quicker against the 'Adobe acrobat' plugin. Not sure if adobe states the different plugin for both the applications anymore.
Not sure if this will work as I don't have a Mac.
Type "chrome://plugins/" into the address bar.
Find the entry marked "Chrome PDF viewer" and click on the Disable link below.
You may also need to disable the "Adbbe Acrobat" plugin if you don't want the PDF opened in a window inside Chrome.
Chrome will now download PDF files, and launch them in your default PDF viewer when you click on the downloaded file at the bottom of the screen.