The problem experienced by the user [here](https://superuser.com/questions/663949/warning-message-acropdf-dll-when-i-try-to-display-a-pdf-document-within-the-we) is similar to what I get in that I receive a prompt: "This webpage wants to run 'AcroPDF.dll'. If you trust this site, you can disable Enhanced Protected Mode for this site to run the control."
![IE10 AcroPDF.dll EPM error](https://i.stack.imgur.com/ZuWMH.jpg)

I understand the prompt can be removed by by disabling EPM but my major concern is actually how to view a PDF when the "Always ignore" button has been clicked. I haven't been able to find a way to undo this and a couple of users have accidentally selected the option since IE 10 was rolled out.
When a user clicks on a PDF after the "Always ignore" button has been checked for that website they only ever see a black box with a cross.

![missing pdf after clicking "Always ignore" in IE10](https://i.stack.imgur.com/WCduy.jpg)

Tried so far:

* Uninstalled & reinstalled IE10
* Checked for entries in HKEY\_CURRENT\_USER\Software\Microsoft\Internet Explorer\Safety
* Performed a repair on Adobe Reader from the menu options.
* Completely reinstalled Adobe Reader
* Deleted temporary internet files
* Disabled EPM after the pdf had been ignored.