I'm using PDF-XChange Viewer as pdf reader.
And all pdf file type cannnot be opened. And it is not only happened in 1 PC, other PCs which are using Avast Pro 4.8 with this false position problem.
I need to turn off Avast protection function and make opening the PDF files correctly.
As the same time, I tested it with Avast Pro 6.0 and using same virus definition. It seems no problem for opening Pdf files.
So, I think it is just caused the problem in using ver 4.8