The *.ACD format is a proprietary archive file and the only thing besides RSLogix 5000 that can open it is RSLogix 5000 Compare. You can use the compare tool to convert the file to L5K or L5X in order to see the program in ASCII format and you can probably get the compare tool for free. I think you can actually view the project in graphical, ladder logic form using the compare tool as well. Again, I'm not positive, but I think the compare tool is free.
The older file formats like *.RSS were standard archive files that you could open with 7zip or similar archive program and view. By view, I mean see the ascii form of the project.