Since version 8.0.552.215, Chrome comes with its own PDF viewer which replaces the default Adobe PDF. This viewer is generally good and we would recommend you leave it enabled unless you are having specific issues.
The following are known issues which may occur:
Intermittent flashing to black on book images.
To revert to the Adobe Reader PDF viewer plugin:
Download the latest Adobe Reader. You may do this here
In the Chrome address bar, type chrome://plugins
Click "Disable" on "Chrome PDF Viewer"
Click "Enable" on "Adobe Reader..."
You may now browse to the image which you were previously having issues with