I managed to get this working by reading an on-line blog and some guess work. I reproduce it here for anybody that might have the same issue. This involves a minor registry edit so if you are not comfortable tweaking the registry, don't try this at home. The blog where I found this procedure suggested that it works on all misbehaving add-ons, but I only tried it for Acrobat. Your mileage may vary.
My problem was that IE11 was not automatically loading the PDF Reader module even though I had it enabled so I had to start by finding the Class ID of the add-on. You can find that by going to Tools, Manage Add-Ons, selecting the offending add-on (you might have to use the "Show All Add-ons" to see it), right click it, then choose More Information. That pulls up a window where you can see the Class ID. For my add-on the value was:
{CA8A9780-280D-11CF-A24D-44553540000}
You cannot copy and paste from that screen to the clipboard so you will need to carefully write down the Class ID. You will need an old-school analog input device like a pencil for that step (I know, so 20th century
).
Next, go to the registry and find this entry:
HKEY_CURRENT_USER\Software\Microsoft\Windows\CurrentVersion\Ext\Settings\
and see if there is an add-on listed under Settings with a matching Class ID. I did not have a matching key so I needed to create one.
I added the missing key under Settings and then created a new DWORD value under that key. The DWORD is named "Flags" and needs a numeric value of 1 to enable the add-on or 0 to disable it. I wanted to use the add-on so I put in a value of 1.
Also check this registry entry:
HKEY_CURRENT_USER\Software\Microsoft\Internet Explorer\Main\TabProcGrowth
and see if it exits. If the value is set to 0 or is missing it will cause a problem. Unlike the other key described above, which needs a DWORD value, if this entry is missing create a new
String value of 1.