MS is back with a new Microsoft Dynamics GP 2013 Service Pack 2: Feature of the Day
this time with improvements to Doc Attach.
Microsoft Dynamics GP 2013 Service Pack 2: Feature of the Day: – Inside Microsoft Dynamics GP – Site Home – MSDN Blogs
Install, Upgrade & AdminTips & Hidden FeaturesMicrosoft & the GP EcosystemGP 2013
Archived post from 2013. Dynamics GP and the links it points to have changed since; check current documentation before relying on version-specific steps.