Google (Chrome) has removed Adobe Reader plugin support from their browser.
According to the Chrome forum
In April 2015 (Chrome 42) NPAPI support (used by Acrobat) will be disabled by default in Chrome and we will unpublish extensions requiring NPAPI plugins from the Chrome Web Store. All NPAPI plugins will appear as if they are not installed, as they will not appear in the navigator.plugins list nor will they be instantiated (even as a placeholder). We will provide an override for users ( chrome://flags/#enable-npapi ) until September