Microsoft breaks WPF printing with .NET update

Microsoft's August 2026 .NET Framework update may have broken printing functionality in Windows applications, particularly those written in WPF (Windows Presentation Foundation). After installing the update, some users reported experiencing System.IO.FileFormatException errors when printing or generating PDF/XPS documents using certain fonts, including the default Calibri font.

The cumulative update for .NET Framework, released on August 11, addressed various issues but also introduced printer problems for Windows 10 and 11, as well as Windows Server 2012 through 2025 versions.

Microsoft has provided a workaround to address the problem: modifying the application's configuration file to disable a security feature called Switch.MS.Internal.TtfDelta.DisableCmapAndSbitOverflowProtection. However, enabling this switch disables security protections and may expose users to previously addressed vulnerabilities. Microsoft advises using this workaround only as a temporary solution, only when necessary to resolve the printing issue.

The company is still investigating the root cause of the problem. The mention of "certain fonts" suggests that the issue may be related to how WPF applications process and handle fonts during XPS/PDF content generation. The recent trend of Microsoft updates breaking systems continues, with the August 11 security update for Windows reportedly causing issues with games that utilize RGB lighting features in peripherals or internal device components.

Microsoft has provided a registry edit to disable the suspected driver, inpoutx64, to resolve the game crashes, but modifying the Windows registry carries inherent risks. As for the printing issue, the only available workaround is to turn off the security protections introduced in the August 2026 update when affected applications require printing on patched devices.