Every time I open a new document in the pdf x-change viewer, it gets opened in the same window. I want to place different documents on different places on the screen (independently of each other, not just tiling the window for side-by-side view), but cannot do it. Even going to the start menu and starting the reader again doesn't open a new instance of the application. Can I force the program to open a new instance or a new independent window?

If this is impossible, which other free reader does what I need and also lets me make changes to the file? I don't need to edit the text itself, but I want to be able to add comments, underline and highlight text, and add some graphic elements (e.g. a circle or a freehand line).