Refer to Collecting Submissions Offline for more information.
1. When creating a new assignment, click gear icon to the right of "Assignment Settings":
2. Under “Details & Information”, click the checkbox next to “Collect submissions offline”:
3. Click “Save” at the bottom of the Assignment Settings window:
4. By default, the assignment will be hidden from students. Customize the visibility settings in the dropdown menu in the top right corner:
When students open the assignment, Blackboard will inform them that the instructor will be collecting submissions offline, but their grade will still be accessible online: