Microsoft: August updates break printing, PDF export in WPF apps

Microsoft confirmed that the August 2026 .NET Framework cumulative update breaks printing and PDF/XPS generation in WPF applications (System.IO.FileFormatException when using certain fonts such as Calibri) across Windows client and server platforms; a temporary workaround using an AppContext switch in the application config is available but disables security protections introduced by the update, potentially exposing systems to attacks while Microsoft investigates a permanent fix.