You can upload documents to cases in two separate areas - via the Add Correspondence quick link or via the Correspondence section of the case.
Go to the Correspondence section of the case and click on Add Correspondence; or
Click on the Add Correspondence quick link in the header
Select the Type of document: Case Note
Select an appropriate documentation Sub Type
Enter text for your note Title and Body
Click the Save as Draft button if you want the ability to edit the note or click the Send + Complete button if you want the note to be view only (no future edits). This will save the note; it will not be sent to anyone.