This action closes the opened document. The opened document will be closed automatically when a task is executed. As it was said before, the automatic saving does not occur. If you need to save the changes in the document, use the action Excel Save Document before the closing of the document or the ending of the task.
If you want to open two different documents in the task, at the beginning close the first document and then open the second one by means of the Excel Open Document.
Excel Open Document
Excel Get Cells
Excel Set Cells
Excel Save Document