Due to phasing out of support for NPAPI plugins, even though you’ve disabled Chrome native PDF viewer in Google Chrome, it still doesn’t allow to open PDF files inline through the plugin of Adobe Reader installed on your computer.
Chrome blocks Adobe PDF plugin by default and displays “Adobe Reader is not allowed” error (update: now showing ‘Adobe Reader needs your permission to run’ message) and asks for your permission to run it. And hovering over the icon in address bar shows “the plugins were blocked on this page “.
For that time, you can select always allow plugins on that site or right click on the Plugin icon and select “Run this plug-in”. Both actions don’t solve the problem permanently and when you get another PDF file in Chrome, you’ll encounter the same error.
Google to Permanently remove NPAPI Support from Chrome in September 2015
At present, you can find this happening in Chrome Canary and soon on beta and stable channels from January 2014.
Google Chrome to Open Downloaded PDF Files in It by Default
Fixing Adobe Reader is not allowed or chrome blocks third- party PDF plugins, to allow them always
If you don’t like viewing PDF files in Chrome PDF viewer and wants them displayed from third-party PDF Reader, then you need to follow below steps.
1. Visit chrome://plugins in Chrome.
2. For Adobe Reader Plugin, select “Always Allowed”
Chrome: “Some parts of this PDF document could not be displayed. Install Adobe Reader?”
Similarly, if you’ve installed Sumatra PDF or Nitro PDF Reader for Chrome instead of Adobe Reader, for Chrome to always open PDF files in them you need to visit chrome://plugins page and need to select “always allowed”.