How to Fix PDF Preview Not Showing in Windows File Explorer?

Windows by default shows the preview of documents, PDF files, and images when viewed in File Explorer. You can toggle the preview pane by clicking the “Preview” button on the toolbar or selecting it from the “View” menu. This preview works for all the files you create without any problem. However, if you download a PDF file from the internet, Windows File Explorer will prevent it from being previewed. In this article, we will explain why Windows blocks the preview, how to unblock the file to enable the preview.

PDF Preview Blocked in File Explorer

Instead of showing the document’s preview, you will see this warning:

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.

PDF File Preview Blocked in File Explorer

This problem was started after Windows 25H2 update. Whenever you download a file from a web browser, email attachment, or another online source, Windows adds a security identifier called the “Mark of the Web” (MOTW). This mark tells Windows that the file came from an untrusted location. As a result, some applications, including the File Explorer Preview Pane, refuse to display the file preview to protect your computer from malicious content. Since this is a built-in Windows security feature, you don’t need to be suspicious about the file’s content. If you trust the file, you can easily remove the security mark and restore the preview. If needed, you can also enable the protection again later.

1. Unblock a Single PDF File

This is the easiest and safest solution.

Open File Explorer and locate your PDF file.
Right-click on the PDF file and select “Properties”. Alternatively, select the file and press Alt + Enter keys.

Stay on the “General” tab and look for the “Security” section at the bottom of the window.
Check the box labeled “Unblock”.
Click “Apply” and then “OK” button.

Close and relaunch the File Explorer.
Select your PDF file and the Preview Pane should now display the document normally.

2. Unblock Multiple Downloaded Files

If you have many downloaded PDF files, you can unblock them all at once using Windows PowerShell.

Open Windows PowerShell and change the prompt to the folder containing the files.
Run the following command to unblock only PDF files in the folder:

Get-ChildItem *.pdf | Unblock-File

Use the following command to unblock every file in the folder:

Get-ChildItem * | Unblock-File

If there are subfolders, use the following command to include files inside subfolders:

Get-ChildItem -Recurse | Unblock-File

Only use these commands if you trust every file in the folder.

3, Enable PDF Preview for All Files

If you wanted to enable the PDF previews (which was the case before 25H2 update), then follow the below steps. Make sure to backup the registry before making changes.

Press Win + R keys, type regedit and press “OK” button to open Registry Editor app.
Copy paste the following path in the address bar and press Enter to navigate to that location.

Computer\HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Windows\CurrentVersion\Internet Settings\Zones\3

Find 180F key and double-click on it.
Change the “Value Data” from 3 to 0.
Click “OK” button and close the Registry Editor app.

Restart your computer and check the File Explorer. You should see the preview is enabled for all downloaded files including PDFs.

How to Enable the Security Again?

When you unblock as explained above (except through Registry Editor), Windows will remove the security mark and you will no longer see the “Unlock” option in file properties. If you want Windows to block the preview again, you need to restore the Mark of the Web. The simplest method is to delete the unblocked copy and download it again. Windows automatically applies the security mark to newly downloaded files. Otherwise, you can manually restore the security mark by using PowerShell app.

Open PowerShell and paste the following command. You will see a warning that the command contains multiple lines and click “Paste anyway” button. Make sure to replace the path with your PDF file’s location.

Set-Content -Path "C:\Path\YourFile.pdf:Zone.Identifier" -Value @"
[ZoneTransfer]
ZoneId=3
"@

This will add the Zone Identifier value as 3 to the file and force Windows treats the file as if it was downloaded from the internet.
Close the File Explorer and relaunch again. Select the PDF file and you will see the warning appear again in the Preview Pane.

If you have unblocked the preview using Registry Editor for all the files, simply follow the same steps and change the “Value data” of 180F key to 3. Restart your system and Windows will block the previews again in File Explorer.

Should You Disable This Protection?

Generally, no. The warning exists to help protect your computer from malicious files downloaded from the internet. You should only unblock files that come from trusted sources, such as your own downloads, coworkers, or reputable websites. Even if you received the PDF files from trusted source, unblocking individual files is a better approach than bulk unblocking. Also, make sure to scan the downloaded files with antivirus software before you unblock them. If the Preview Pane still doesn’t work after unblocking, ensure a PDF reader such as Adobe Acrobat or Microsoft Edge is properly associated with PDF files.