Microsoft's August Updates Break Printing, PDF Export in Some WPF Apps
Microsoft has confirmed that its August .NET Framework updates have broken printing and PDF export functionality in some Windows applications.
The issue, which affects only apps using the Windows Presentation Foundation (WPF) UI framework, causes a System.IO.FileFormatException when printing or generating PDF/XPS content that uses certain fonts, including Calibri.
According to Microsoft's Windows release health alert, this problem affects both client and server versions of Windows, from Windows Server 2012 up to Windows Server 2025, as well as the latest versions of Windows 10 and Windows 11.
Microsoft is still investigating the issue but has provided a temporary fix for affected users. This workaround involves enabling the Switch.MS.Internal.TtfDelta.DisableCmapAndSbitOverflowProtection AppContext switch in the application config file, which will disable protections introduced with the August .NET Framework update and expose the system to potential attacks.
Microsoft warns that this workaround should only be used as a temporary measure when necessary to address the issue.