Microsoft has confirmed that .NET Framework updates shipped with the August 2026 Patch Tuesday are causing printing and PDF export failures in some applications. The issue affects software built on the Windows Presentation Foundation (WPF) UI framework, an open-source graphical subsystem used for Windows desktop client apps. According to a Windows release health alert, affected WPF applications may throw a System.IO.FileFormatException when printing or generating PDF/XPS content that relies on certain fonts, including Calibri.
The problem impacts a wide range of Microsoft platforms, spanning both client and server releases. On the client side, the affected systems include the latest versions of Windows 10 and Windows 11. For servers, the range extends from Windows Server 2012 through Windows Server 2025, covering most supported versions in the lineup.
Microsoft says it is still investigating the root cause and has not yet delivered a permanent fix. In the meantime, the company has provided a temporary workaround for users who need to restore printing and PDF export functionality. The solution involves enabling a specific AppContext switch in the application configuration file, which requires adding a line that sets Switch.MS.Internal.TtfDelta.DisableCmapAndSbitOverflowProtection to true.
However, Microsoft warns that activating this switch disables protections introduced with the August 2026 .NET Framework update. That means systems using the workaround could be exposed to attacks that exploit the vulnerabilities addressed by this month鈥檚 security patches. The company explicitly advises using the workaround only as a temporary measure and only when necessary to resolve the printing issue.
This is not the first time WPF has caused problems after a Microsoft update. Roughly five years ago, in February 2021, Microsoft addressed a separate known issue that led to crashes in WPF apps and Visual Studio following the installation of Windows 10 cumulative updates. That earlier incident was resolved with a corrective update, though no permanent solution has been announced for the current font-related printing failures.
Separately, Microsoft also shared a temporary workaround on Friday for another known issue tied to Windows 11 updates from the August 2026 Patch Tuesday. That problem affects specific games, including ARC Raiders, MARVEL T kon: Fighting Souls, and The Finals, causing them to crash or freeze. The company did not indicate when a permanent fix might be available for either the WPF printing issue or the game-related problem.
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