I don't know how I did it (need to look) but somehow when I open a PDF via the downloads section in Chrome, it opens in both Chrome and Adobe :?
Having said that, you cannot split between the two if you double click on the file. It will go to your default application. With extra steps, I would recommend Beers's suggestion once it's downloaded.
But if you don't want to have extra steps, I would say only open in the browser if you are just viewing/printing, unless you a) have an Adobe subscription with Acrobat and you need to edit PDFs, or b) you are trying to view a form that the browser's PDF cannot read properly. It's been a long while but this was something of an issue when I was working for an university where they had PDF files that were forms with special items (drop downs I think, or some formula/script) and the browser said to download Adobe Reader (which was installed... and the default) so the resolution was to download the file then open the file.