Step 1: Unblock all already downloaded PDF files.
Open PowerShell as Administrator and run:
Unblock-File -Path "C:\Users\admin\Downloads\*.pdf"
Replace admin with the actual path where your files are downloaded.
Step 2: Prevent Windows from setting the "file is blocked" flag for newly downloaded files.
1. Open Registry Editor (Win + R > type regedit) and navigate to: Computer\HKEY_CURRENT_USER\Software\Microsoft\Windows\CurrentVersion\Policies\
2. Create a new key named Attachments.
3. Inside it, create a new DWORD (32-bit) value called SaveZoneInformation and set it to 1.
Alternatively, you can do the same via Group Policy Editor (Win + R > type gpedit):
User Configuration > Administrative Templates > Windows Components > Attachment Manager > Do not preserve zone information in file attachments > Enabled
Step 3: The same issue can happen when opening PDFs from shared network locations.
In that case, do the following:
Press Win + R, type inetcpl.cpl, and open the Security tab.
Select Local intranet > click Sites > check Automatically detect intranet network.
You can also click Advanced, then add the required network IP range manually — for example:
192.168.1.* > click Add.