I've checked various websites, but I couldn't find anything related to file copy procedure, which means that this function might not be available. However, you can simply select a text and right click it. If no option appears, then the software acts exact like the name says: like a viewer without the possibility to copy the text.
However, if you have the Print function enabled, install CutePDF Writer and then print to PDF. I've recommended this because you can copy from the PDF files since CutePDF outputs files without security permissions.