You can copy the whole file. But for parts of the contents you probably need to use the menu copy option rather than just highlight and grab. They are strange, in order to view all sorts of formats they are surrounded with loads of control stuff you don't normally see. Try the menus and see where that gets you.
Wasn't a text "attachment" in the original document you were trying to copy was it ? I've seen PDL files where the search function couldn't find a word I was looking at, apparently because of that.