Microsoft's August 2026 .NET update breaks printing and PDF export in WPF apps

Microsoft has confirmed that the August 2026 .NET Framework cumulative update causes some WPF-based applications to throw a System.IO.FileFormatException when printing or exporting to PDF/XPS with fonts like Calibri. The bug affects current Windows 10 and 11 releases as well as Windows Server versions from 2012 through 2025, and Microsoft is still working on a permanent fix.