File preview in Windows 11

[jctech2025]

Hi All,

I saw other threads on this issue where no one can preview PDF files in Window Explorer.  I did a bit of troubleshooting and notice that is it only PDF files.  Even after reinstalling I still get the same results for all the staff members: 

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 it’s contents.

Where would this be coming from?

[Meenakshi Negi]

Hi jctech2025,

Thank you for reaching out, and sorry about the trouble caused.

As the user gets an error message when opening files in preview, please check if the files are saved locally. Also, check if it happens with all PDFs. Try creating a new test PDF and then trying to open it in preview.

We would require more information to investigate this behaviour further. If you can share the screen recording, we can try replicating this issue. 

Please share the Acrobat and OS version in use.

Thanks,

Meenakshi

[Jim_Rick6879]

You might want to check the Windows Preview Handler settings — this warning usually comes from Windows Security, not Acrobat.

Here’s what helps in most cases:

1. Reset the PDF preview handler:

• Open File Explorer → View → Options → View tab.

• Uncheck “Always show icons, never thumbnails” and apply.

• Then open Settings → Apps → Default Apps → Choose defaults by file type → .pdf → Adobe Acrobat.

2. Re-enable PDF Preview in Acrobat:

• Go to Edit → Preferences → General → Enable PDF thumbnail previews in Windows Explorer.

• Restart your computer afterward.

3. Check the registry flag (for advanced users):
Sometimes Windows marks PDFs as unsafe if the handler path got altered. Running an SFC /scannow command from CMD can reset this.

This issue started appearing after a few Windows 11 updates, so refreshing the handler link to Acrobat usually clears the warning.       

[Celine36808554op3a]

this was intentional by microsoft and it is horrible. 

[Jordan$]

Agreed. I'm convinced Microsoft hates creatives. Just like their terrible ACM, they take a sledgehammer approach to a complex issue that needs a scapel.

[ph�_2423]

According to the information from the KB5066791 update released on October 14, 2025, Microsoft has strengthened security measures for Windows 10, especially regarding the handling of files downloaded from the Internet.

🔐 Related content in KB5066791:
File Explorer automatically activates protection mode for files downloaded from the Internet or unknown sources.

When you try to preview or open these files, the system will display a warning as shown in the image you sent: “The file you are trying to preview may harm your computer…”

The goal is to prevent malicious code or dangerous software from being activated through the preview operation.

How to fix if you want to disable this feature:

You can unblock the file in the following way:

Right-click on the file → select Properties

In the General tab, if you see the line “This file came from another computer and might be blocked”, click Unblock.

Click OK to save the changes.

Unblock Multiple Files Using PowerShell
📌 1. Open PowerShell with administrative privileges
Press Windows + X → select Windows PowerShell (Admin)

📄 2. Run the following command to unblock all files in a folder:
powershell
Get-ChildItem "C:\Path\To\Folder" -Recurse | Unblock-File
🔍 Explanation:

Get-ChildItem: get a list of all files in the folder

"C:\Path\To\Folder": replace with the actual path to the folder containing the file you want to unblock

-Recurse: applies to subfolders

Unblock-File: command to unblock files

[JO-CPA]

Microsoft should have blocked PDFs when it first came out... would have saved the world from a LOT viruses in PDFs... (and should have done the same for Flash for that matter).