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Microsoft says August 2026 .NET updates break printing and PDF/XPS export in WPF apps

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Summary

Microsoft says August 2026 .NET Framework updates can cause some WPF apps to fail when printing or creating PDF/XPS content with certain fonts. A temporary workaround disables protections added by the update; a permanent fix is pending.

Key points

  • Some WPF applications may fail with a System.IO.FileFormatException when printing or generating PDF/XPS content using certain fonts, including Calibri.
  • The issue affects Windows client versions and Windows Server releases from Server 2012 through Server 2025.
  • Microsoft is investigating and has provided a temporary AppContext switch workaround.
  • Microsoft warns the workaround disables protections added by the August update and could expose systems to attacks exploiting vulnerabilities addressed by that update.
  • Microsoft recommends using the workaround only temporarily and when needed; a permanent fix has not yet been released.

Article Details

Event Type
August 2026 .NET Framework cumulative update regression affecting printing and PDF/XPS export in some WPF applications.
Impact
Affected applications may fail with a System.IO.FileFormatException when printing or generating PDF/XPS content using certain fonts, including Calibri. The issue affects Windows client releases and Windows Server 2012 through Windows Server 2025. Microsoft provided a temporary AppContext switch workaround, but warned that it disables protections added by the update and may expose systems to attacks exploiting vulnerabilities addressed by the security updates.

Vendors

MicrosoftMicrosoft confirmed that the August 2026 .NET Framework cumulative update is causing printing and PDF/XPS export failures in some WPF applications, with errors affecting certain fonts such as Calibri.

Products

.NET FrameworkMicrosoft confirmed that the August 2026 .NET Framework cumulative update is causing printing and PDF/XPS export failures in some WPF applications, with errors affecting certain fonts such as Calibri.Windows 10The complete list of impacted platforms includes both Windows client releases (including the latest versions of Windows 10 and Windows 11) and Windows Server (from Windows Server 2012 up to Windows Server 2025).Windows 11The complete list of impacted platforms includes both Windows client releases (including the latest versions of Windows 10 and Windows 11) and Windows Server (from Windows Server 2012 up to Windows Server 2025).Windows Presentation Foundation (WPF)The issue affects apps built with the Windows Presentation Foundation (WPF) framework.Windows ServerThe problem impacts Windows client and Windows Server versions from Server 2012 through Server 2025.

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