Yes - you can save a presentation that will be uploaded into the BigBlueButtonBN room/activity when the conference is live.
As the owner or administrator of a course, when you create or edit a BigBlueButtonBN room/activity with a document that will be available in the live BigBlueButton session.
To upload a document navigate to the presentation content menu; drag and drop your file into the uploader window or select the file upload icon.
The file picker provides several different sources/options to access your content from. Once you have chosen a document choose upload file.
Important: the specific options within the file picker will vary based on the Moodle course settings.
When the BigBlueButtonBN room/activity is live the uploaded content will be displayed as the default presentation.