Open Adobe Reader. Click on edit. Click on preferences. Click on internet about half way down on the left. If you do not have an oprion there that says open adobe in browser then there should be a link in there to show you how to check your addon and ensure it is working properly. The link will take you here: http://helpx.adobe.com/acrobat/using/display-pdf-browser-acrobat-xi.html

In Adobe Reader:

1. Click on Edit
2. Click on Preferences
3. Click on Internet (about half way down on the left).
4. You should either have:
   • a) An option that says open adobe in browser
   • b) There should be the following link to show you how to ensure the addon is working properly.
     • http://helpx.adobe.com/acrobat/using/display-pdf-browser-acrobat-xi.html

In Internet Explorer 9: ^{(according to the link above)}

1. Open Internet Explorer, and choose Tools > Manage Add-ons.
2. Under Add-on Types, select Toolbars And Extensions.
3. In the Show menu, select All Add-ons.
   

4. In the list of add-ons, select Adobe PDF Reader.
   Note: If you do not see the Adobe PDF Reader add-on, try the other options on the menu. For example, on some systems, the add-on appears when you select Run Without Permission.

5. Click the Enable or Disable button (it toggles depending on the status of the selected add-on):
   Enable sets the Adobe PDF Reader add-on to open PDFs in the browser.
   Disable turns off the add-on so it does not open PDFs in the browser.