ok after reading here, i decided to add hexagon to my arsenal (i'm a carrara5 pro user)...first thing..importing 3ds files....? the pdf writes about extensions......where are these "extensions"

Extensions are the file type letters after the dot in the file name. For example, .hxn is a Hexagon file, .car is a Carrara file. You should see them when you try to import.

Also, if your running windows, you may not be used to seeing extensions because they are turned off by default.  If you want to see them and they are most useful, then start the windows file manager go to tools then folder options then the view tab and take out the button that says to hide known file types.  I think everone should do this  because it's dangerous to open an email attachment containing executible code and how else would you know?