Depending on Document Status
When a Document has just been Created only Document Authors can upload a file to a Document, this means that only Author(s) will see the Upload button when a Document is in Created Status.
Once a file has been uploaded the Edit button will appear. If there is no file to edit the button is not visible.
Once a Document reaches Under Signing by Approver Status the Edit button is no longer visible.
Depending on Roles in the Document
Managers, Regular Users and Read Only Users will only see the Edit button if they have a Role in the Document.
Administrators see the Edit button regardless of having a role in the Document or not.