Like Dave Musgrave, I occasionally point to CustomerSource locations for files. I forget that while most Dynamics GP customers have access to CS, many only give access to one employee. In a new post, Dave takes on CustomerSource and PartnerSource access and how to get it.
CustomerSource and PartnerSource Access
Payables & ReceivablesMicrosoft & the GP Ecosystem
Archived post from 2008. Dynamics GP and the links it points to have changed since; check current documentation before relying on version-specific steps.