From:  Michael Gibson
2595.4 In reply to 2595.3 
Hi Philip, no problem!

Yes other applications can sometimes use those terms "Open" and "Import" slightly differently where different file types are supported between them, with Open only being used for the native file type and Import for bringing in any non-native file type.

In MoI it is not quite like that - in MoI the main difference between these 2 options is the behavior of what is done with any previously existing data.

In MoI "Open" means to discard any current model data and only have the newly read in stuff present. You can do that to any file type but the current file name (which is the file that will be written if you push the "Save" button) is only set when you open a 3DM file.

"Import" on the other hand in MoI means keep any existing data in place and merge newly read in stuff to the current model data. Import does not set the current file name since it is meant to add to the current file rather than replace it.

- Michael