How to disable the downloading of a file

You can choose to disable downloads for any given file

Go to the Files module and then select the document you wish to prevent from being downloaded
To check that the PDF is currently available for download, click on the three dots connected by a line (the sharing button)
Then click on the 3 horizontal dots "..." to view the drop-down menu, and click on the Access button
Select the Rules button
Enable the Prevent download button to disable downloads on the desired file