Mark Files Private

In Salesforce, Files are by default public to anyone who has access to the record with the File attached.

To mark the File as Private:

1. Navigate to the Files section of the Record.
   
2. Click the link of the file you want to mark Private.
   
3. Select the menu button, then select Edit File Details.
   
4. You can edit the privacy settings of the File to Private on Records, meaning the File will need to be manually shared with other users by the File owner.
   
5. You can also add update if the File can be shared or not.
   
6. Select Save to save your changes.  Now the File is only visible by the File Owner and Salesforce Administrators.