Unless you’ve disabled Chrome PDF Viewer soon Google Chrome, starting Chrome Canary will open downloaded PDF files in it by default. Google thinks PDFs are safer to open in the browser. Of course, Chrome will still offer the option to open that PDF file in third-party PDF Reader application you’ve installed on Windows by offering "open with system viewer "option which appears when you right-click on file on download shelf at the bottom.

open with system viewer Chrome PDF

"PDFs in particular are safer to open in the browser. This patch changes the handling of downloads to open such files in the browser by default instead of the system handler for the file type. A "Open with system handler" menu item will be available so that users can still use the
system application if needed."

Google already phased out support for NPAPI plugins which means Chrome blocks Adobe PDF plugin by default and shows Adobe Reader is not allowed message, we’ve covered how to allow it.

FYI If Chrome PDF Viewer can’t display any PDF properly in it, it displays message on top to open it in Adobe Reader or install it.

Is it time to make Google Chrome default PDF Reader on your computer?. Found via [Francois]