You require to save your drawing to be opened in a previous version to be edited. When you choose to save the file as 16.0, then open the drawing in CorelDraw Suite X6, a message is produced that the file was created by a Pre-Release Version of Draw.
This message will only appear, if your version of CorelDraw X6 is not updated to 16.4. Earlier versions below 16.4 will produce the Pre-Release message. To correct this issue please visit the following website: