Amber IT Alert - A Change From Microsoft in Downloading PDF files from the internet. Here’s What You Should Know:
As of October 2025 Microsoft has pushed a security update that changes how PDF (and other) files downloaded from the internet behave in Windows 11 and some Windows Server versions…
Note: This update applies for Windows 11 and several Windows Server versions from October 2025 onward. Information source is Microsoft.com.
What’s Changed?
Following recent Microsoft Security Updates (released 14 Oct 2025 or later), File Explorer automatically disables the preview pane for files, including PDFs, that were downloaded from the Internet (i.e. “Internet-origin” files).
When you try to preview such a file you’ll see a warning like:
“The file you are attempting to preview could harm your computer. If you trust the file and the source you received it from, open it to view its contents.”
This includes files stored in cloud-backed folders (e.g. OneDrive / SharePoint) as well as direct downloads, because Windows tags them with the “Internet security zone” flag (technically via something called Mark of the Web - MoTW).
Why Has This Changed?
This change was introduced to block a security vulnerability: previously, previewing certain files (especially ones containing HTML/linked content) could leak sensitive credentials (NTLM hashes) to external resources. The update closes that loophole, to keep you and your business safe.
AQUA IT’s Perspective
This update is important for all business environments: If your organisation receives a steady flow of PDFs from external sources - such as invoices, drawings, or forms - AQUA will help you gently adjust your usual deployment and documentation processes.
AQUA is here to ensure users understand why Windows displays these warnings as part of its security safeguards, and to guide you on when it’s safe to unblock trusted files, so your team can navigate with confidence.
We’ll also help you review whether certain network shares or document locations should be designated as “trusted” within the organisation, allowing your workflow to remain calm and smooth-sailing, without unexpected ripples or interruptions.
AQUA IT are Here to Make this Change Stress-Free!
So, if you ever wonder “Why can’t I preview this file anymore?”, just drop us a message. We’ll help unblock safely or show you alternate ways to view the file without risking your system’s calm.
Don’t hesitate to contact David, Martin, or Siobhan at 0141 530 2007 for quick support, or email aitsupport@aquait.co.uk
We’re here to make your IT stress-free!
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