Release strategy behavior for purchase documents

Hi all,

I'm working at a company that recentily has implanted SAP. We noticed last week that the approved documents, like PR, PO, RFQ etc.. can be modified by the users and that documents doesn't modify its approval status, I mean, they remains approved.

I'd like to know if is there any standard way to configure the SAP to not allow any modification in an approved document, or if an approved document has been modified, it resets its approval status to pending approval again.

Thanks in advanced,

Rodrigo