After Microsoft released updates for Windows 11 on August’s Patch Tuesday, users have been reporting problems with their printers and with the creation of PDFs. Microsoft has now admitted that one of the updates released on Patch Tuesday is to blame.
The problematic update is KB5120708, which isn’t actually for Windows 11 itself but rather affects the .NET Framework.
Microsoft confirms that, following the installation of this update, some applications may encounter errors when printing from documents containing certain common fonts, or when creating PDF or XPS files:
Known Issues: After installing the August 2026 .NET Framework cumulative update, some WPF applications may fail with a
System.IO.FileFormatExceptionwhen printing or generating PDF/XPS content that uses certain fonts, including Calibri.
The matter is still being investigated, but in the meantime you can use a temporary workaround if you’re experiencing these issues:
Workaround: Applications may mitigate the issue by enabling the
Switch.MS.Internal.TtfDelta.DisableCmapAndSbitOverflowProtectionAppContext switch in the app config file, as shown below.This switch disables security protections introduced in the August 2026 update and may increase exposure to the vulnerabilities addressed by that update. Microsoft recommends using this workaround only as a temporary measure and only when required to address this issue.
August 2026’s Patch Tuesday is turning into an ever-growing disaster for Windows 11 users. Yesterday, Microsoft admitted that the KB5121003 update was also causing problems, primarily affecting gamers.
