Error message

Help with this please.

It wasn't sent by email so that is not the issue.

What do i need to download to access further. I am on a Mac.

Adobe Acrobat Reader could not open '231581_QK4_TheWishingTree 2.bak' because it is either not a supported file type or because the file has been damaged (for example, it was sent as an email attachment and wasn't correctly decoded).