You can only approve a document if you have access and are set as an Internal Approver 


Step 1: The approver of the document will get an email & task in their Task Manager to approve. It will look like this below



Step 2: The approver select the task above 

 Step 3: Select Sign Off to approve. If you are not happy input a message and select Requires Review



Step 4: The status is no Completed & Approved