Pam has a nice overview of Doc Attach in her #GP2018 Feature of the Day: Document Attach in Summary – Microsoft Dynamics GP Community
#GP2018 Feature of the Day: Document Attach in Summary – Microsoft Dynamics GP Community
Tips & Hidden FeaturesMicrosoft & the GP EcosystemGP 2018
Archived post from 2017. Dynamics GP and the links it points to have changed since; check current documentation before relying on version-specific steps.