Hi Sravan ,
Are you looking at having a new content item itself (as in a new entity) from a workflow ? I am not sure if that would be possible since when a WF starts for a document , it is for that particular context .You can replace the existing item which initially was uploaded .
This is how it works, when a content is in a workflow step the approver can edit the content and replace it with an edited content for further steps (provided the workkflow step allows edit) and this edited document will be release when it comes out of the workflow. The other possibility is when a user (need not be approver of a step) creates a new revision of the same content whose latest revision is already in a workflow, this is possible and both revisions will be in the workflow, although the recent revision (now the latest revision) gets precedence and will be available for search.
Hope this helps.