Windows cannot open or copy a .DAT file (originally a .DOCX) after reinstalling Windows \u2013 shows encryption/permission error

[Mike Lynch 0]

I had a normal .DOCX file in my previous Windows installation. A long time ago, I manually changed its extension to .DAT (I did not use encryption or EFS).

After reinstalling Windows (clean install), Windows now refuses to:

• open the file
• copy it
• rename it
• or open it even after changing extension back to .DOCX

Windows shows a message related to encryption or permission, as if the file is locked or encrypted.

Important notes:

• I never enabled “Encrypt contents to secure data”
• The file was inside my previous Windows user profile
• I no longer have access to the old Windows user or the old SID
• Even with antivirus (NOD32) disabled, the behavior is the same
• Other files copied from the old Windows work fine — only this .DAT file is locked

It looks like Windows thinks the file belongs to the previous user SID or considers it encrypted, but I cannot decrypt or take ownership.

How can I regain access to this file? Is there any method to override the encryption/permissions or recover the file contents?