approval workflow is not working?

Could it be that you still need two more approvals for the document? Document approval could be set to All at once (in parallel) so there are three approval tasks. One is completed, two remain.

You could try changing this to 'Serial' instead if you would rather tasks are only set one at a time, in a chain. It is also worth checking to see if Expand Groups is ticked - if it is, then an approval task will be set to each member of an approval group. As you see in the picture below, I have two approval groups instead of people; when active, the Expand Groups setting assigns a task to each group member. If it is not active then a single person from a group can approve the document on behalf of the group.

On your document library -> Workflow Settings -> Select your approval workflow ->