Improve "Save a copy" functionality to "Export document"

The current implementation of "Save a copy" is the next:
1) All document's objects are cloned in memory into a new document.
2) The new one is saved to a file.
3) The new one is added to the project
=> The document, added to the project, could be not compatible with the saved file because it is not read from the last. And it could contain some information that is not stored in the file. It could lead to some confusions.

Expected decision:
Save the source document to the file, then read the file into a new document and add it to a project.
So, this functionality could be renamed to "Export document".