Adobe Reader could not open 'PO 6484.pdf' 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).

Some one send me documents, but I can not open them and this is the message I get: Adobe Reader could not open 'PO 6484.pdf' 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).

Can anybody help?

Note: I only see the Adobe logo