Projects remain open until you close them or exit the program. You can close the active project without exiting the program. If you have more than one drawing open, make sure the drawing you want to close is the active one.
To close a drawing:
Select File
> Close, or click the Close button on the Standard toolbar.
In the dialog, click Yes or No when you are asked to save changes.
If you haven’t named the project yet and you clicked Yes in the previous step, specify a name for the project in the Save As dialog, then click Save.