Document Toolkit users, please take note of the following;
Microsoft released a security patch on Tuesday, December 11th which introduces an issue related to rendering OpenType Fonts. After installing the KB2753842 patch, OpenType fonts with postscript outlines are no longer rendered. The issue appears in any application using these fonts, among others PowerPoint and Silverlight are affected.
When you use Document Toolkit in your Silverlight application, you will also be affected. Documents are no longer correctly rendered. Uninstalling the KB2753842 patch seems to solve the render issue. However, uninstalling the patch leaves you vulnerable to the security issue the patch is solving. We therefor do not recommend uninstalling the patch.
Microsoft has confirmed there is an issue with the security update;
"We are aware of issues related to OpenType Font (OTF) rendering in applications such as PowerPoint on affected versions of Windows that occur after this security update is applied. We are currently investigating these issues and will take appropriate action to address the known issues."
This post will be updated when new information becomes available.
Update 12/21: Problem solved. Microsoft has rereleased security update 2753842 with a fix for the font rendering issue. From the security bulletin:
"The original version of security update 2753842 had an issue related to OpenType Font (OTF) rendering in applications such as PowerPoint on affected versions of Windows. This issue was resolved in the version of this security update that was rereleased on December 20, 2012. "
After installing the new version of the security update, font rendering issues no longer occur in Document Toolkit.