You mean Editing Document after it has been created and attached to the case?
I don't think you can edit a document after creation in any case. Agent can Edit document in Workspace before generating it.
What exactly is your requirement for this situation? Editing the document after creating it would beat the purpose of document auto-generation.

We had a requirement for the Agent to add information to the document in particular cases, so we created a variable in Record Producer that would tell us weather the Agent involvement is needed or not. If it was not needed, the document gets auto-generated, but if the document needs to be edited, a case gets created and agent can work on it and edit the document.