Problem download and reading PDF doc.sent to me

[Mesug]

Normally, all PDF docments sent to me through attachment to my email could be downloaded and read. However, I encountered some problems recently when I received a message with PDF document attached thereto which I could not download and read as I used to do. My Adobe Reader software is updated, yet I still could not download and read it even if it's already preparely scanned by my Northon Antivirus as safe document. What should I do to solve this problem. Please help me. Thank you. Mike