Tech Entertainer

Windows Printing or PDF Export Broken After the August 2026 Update? How to Fix It

By Tech Entertainer Team · 2026-08-28

If an app on your Windows PC started throwing a printing or PDF export error this week, a .NET Framework update is the likely cause. Microsoft shipped it on August 11, 2026, and it broke printing and PDF/XPS generation in a specific class of Windows applications. The fix depends on which app is failing and how much control you have over it.

What Error Are You Seeing?

If this bug is hitting you, the app throws a System.IO.FileFormatException the moment you try to print a document or export it to PDF or XPS. The crash happens mid-action, often with the document already open and formatted correctly on screen. It only shows up in apps built with Windows Presentation Foundation (WPF), Microsoft's .NET framework for desktop app interfaces.

The trigger is font-specific. Documents using Calibri or Cambria are the confirmed culprits. If your document uses Arial, Times New Roman, or most other standard fonts, you likely won't see this at all, even on an affected machine.

Why Did This Start Happening?

Microsoft's August 11, 2026 .NET Framework cumulative update added overflow protection for how WPF reads certain data inside TrueType font files, specifically the cmap and sbit tables. This protection is a security fix. It closes a vulnerability tied to malformed font data.

The side effect: some legitimate, unmodified fonts, including Calibri and Cambria, trip the new protection and get rejected instead of accepted. The app doesn't know how to recover from this rejection, so it throws the FileFormatException and the print or export job fails outright.

This is confirmed in Microsoft's own support documentation for the update, and it affects any machine running an affected KB, not a specific brand of printer or PDF app.

Which Windows Versions and Updates Are Affected?

The updates responsible are the August 11, 2026 .NET Framework cumulative updates:

  • KB5120708 – Windows 11, version 25H2, and Windows Server 2025
  • KB5120710 – Windows 11, version 24H2
  • KB5120705 – Windows Server 2022

Microsoft's guidance also lists Windows 10 and Windows Server releases back to Server 2012 as affected wherever the matching August 2026 .NET Framework update is installed. If you're not sure which update your PC has, go to Settings > Windows Update > Update history and look for an entry dated August 11, 2026 with ".NET Framework" in the name.

What Apps Does This Break?

Not every program on your PC. This bug only hits applications built on WPF, Microsoft's older desktop UI framework for .NET apps. Common mainstream software like Microsoft Word, Adobe Acrobat, and most web browsers use different print and rendering engines, so they're not affected by this specific bug.

You're more likely to run into this with:

  • Internal line-of-business apps built in-house or by a vendor on WPF
  • Accounting, invoicing, or reporting tools generating PDFs through .NET
  • Custom document management or forms software used at small and mid-size businesses

If you don't know whether an app is built on WPF, the fastest test is simple: try printing or exporting the same document with a different font. If switching from Calibri to Arial makes the error disappear, you've confirmed the cause.

How Do You Fix It Right Now?

You have three real options, ranked from easiest to most involved.

Option 1: Change the Font

The fastest fix costs you nothing and needs no technical changes. Open the document template and swap Calibri or Cambria for Arial, Times New Roman, or another standard font, then print or export again. Since the crash is tied specifically to the font's internal table structure, most other fonts print fine even on an unpatched, affected system.

This works well for one-off documents and templates you control directly. It doesn't help if the font is hardcoded into third-party software you don't have access to edit.

Option 2: Apply Microsoft's AppContext Switch

If the failing app has its own configuration file, typically named something like AppName.exe.config sitting in the same folder as the executable, you have a way to disable the new protection for it specifically. Open the config file in a text editor and add this inside the <configuration> section:

<runtime>
  <AppContextSwitchOverrides value="Switch.MS.Internal.TtfDelta.DisableCmapAndSbitOverflowProtection=true"/>
</runtime>

Save the file and restart the app. Printing and PDF export should work again with the original fonts intact.

Microsoft states directly this switch turns off the security protection the August update introduced, so it does increase your exposure to the vulnerability the update was designed to close. Use it as a bridge, not a permanent setting, and remove it once Microsoft ships a real fix.

Option 3: Uninstall the August 2026 .NET Framework Update

If printing is business-critical and neither of the options above work for you, such as a vendor app you don't have access to edit and don't want to re-font, rolling back the update itself is a fallback option.

  1. Go to Settings > Windows Update > Update history.
  2. Click Uninstall updates.
  3. Find the .NET Framework update dated August 11, 2026 (KB5120708, KB5120710, or KB5120705 depending on your Windows version).
  4. Click Uninstall and restart when prompted.

This restores full printing function immediately, but it also removes the security patches the update delivered. Only do this if you have no other path forward, and plan to reinstall the update as soon as Microsoft issues a permanent fix.

How Do You Confirm It's This Specific Bug?

Before you spend time on a fix, rule out other causes. A few quick checks separate this bug from a generic printer problem:

  • Check the error text. If the app shows System.IO.FileFormatException, or a crash log or Event Viewer entry references it, this is the specific signature tied to this update.
  • Check the timing. Ask whether the printing or PDF export problem started right after a Windows Update installed in mid-to-late August 2026. If the app printed fine a week earlier and broke without any changes to the printer, drivers, or the app itself, the update is the likely cause.
  • Check the font. Open the failing document and look at what font the body text or a header uses. Calibri and Cambria are the two confirmed triggers. If the document uses neither, this specific bug likely isn't your issue, and you should look at driver or printer spooler problems instead.
  • Check whether the app is WPF-based. You won't always know this from the name alone, but a quick sign is the presence of an AppName.exe.config file next to the executable in the installation folder. Not every WPF app ships one, but if you see one, it's a strong hint you're dealing with a .NET WPF application.

If your printing problem doesn't match any of these markers, it's worth ruling out a stuck print spooler, an outdated printer driver, or a network connectivity issue before assuming this update is to blame.

What Should IT Admins Do Before Rolling This Out Further?

If you manage more than a handful of machines, this bug is worth testing for before you push the August 2026 .NET Framework update to your full fleet.

  • Test on a small pilot group first. Install the update on a handful of machines running your line-of-business WPF apps, then run through your normal printing and PDF export workflows before wider deployment.
  • Inventory affected fonts. Search your document templates, report generators, and invoicing systems for Calibri or Cambria usage. Standardizing on a font like Arial across templates sidesteps the issue entirely and avoids touching app config files.
  • Document which apps need the AppContext switch. If you do need Microsoft's workaround for specific software, keep a list of exactly which machines and apps have it applied, since you'll want to remove the switch once a permanent fix ships and reinstate the full security protection.
  • Watch Microsoft's release health dashboard. The known issue is tracked directly against the KB articles for KB5120708, KB5120710, and KB5120705, making it the fastest place to see status changes before general news coverage picks it up.

Is Microsoft Working on a Permanent Fix?

Microsoft's own support pages for the affected KBs list this issue's status as "Investigating," with no confirmed resolution date as of this writing. There's no indication of whether the eventual fix will come as a follow-up cumulative update or a targeted out-of-band patch.

Until then, check your update history periodically or watch Microsoft's release health dashboard for the specific KB you installed. When a fix ships, you'll want to remove any AppContext switch overrides you added, since the whole point of the original update was closing a real security hole.

Frequently Asked Questions

Will uninstalling the August 2026 update fix printing for good?

It restores printing right away, but it also removes the security fixes the update shipped. Treat it as a short-term step while you wait for Microsoft's permanent patch, and reinstall the update once one is available.

Does this bug affect Microsoft Word or Adobe Acrobat?

No. Word and Acrobat use their own print and PDF engines, not WPF. This issue is limited to WPF-based .NET applications, so most mainstream office software is unaffected. Check the specific failing app before assuming it's this bug.

Frequently Asked Questions

Will uninstalling the August 2026 update fix printing for good?

It restores printing right away, but it also removes the security fixes the update shipped. Treat it as a short-term step while you wait for Microsoft's permanent patch, and reinstall the update once one is available.

Does this bug affect Microsoft Word or Adobe Acrobat?

No. Word and Acrobat use their own print and PDF engines, not WPF. This issue is limited to WPF-based .NET applications, so most mainstream office software is unaffected. Check the specific app failing before assuming it's this bug.