How can i recover a deleted document?
i deleted a document from the nuxeo repository using the method of : removeDocument(docRef).
Now how can i undelete/recover the same document?
You can't, it's been removed from the database. You may have a database backup to retrieve the info you need.
What you can recover is the attached documents, they are still in the
binaries directory unless you've cleaned orphan binaries (in the Admin Center). But you'll need the id(s) of the attached documents, and for that unless you've logged it beforehand you'll also need a database backup. See this for the database structure to help you recover attached files.