Unable to un-encrypt Preview PDF

Hello,

I have a PDF document which I assigned a password to in Preview. When I open the document, Preview accepts my password and I can see the document however, I am not able make and edits to the PDF such as move pages around in the Thumbnail or drag pages from another PDF into the encrypted document.

In the File menu, I select Enter Password and see the green checks next to the 3 permissions. Below it says to enable permissions I have to enter the owner password. The problem is that the field to enter my password is not editable. I've attached a screen shot of this info box.

Can someone tell me what I have missed and what I would need to do to edit this document?

Thanks.

Attached Images

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