In the GDL Editor window ("File/GDL Objects/Open Object") select the "Picture Preview" button at the lower left-hand corner of the dialog. Copy/Paste your desired preview picture. FYI - The preview window only allows 128x128 pixels for the output image.
David Larrew, AIA, GDLA, GSRC
Architectural Technology Specialist
a r c h i S O L U T I O N S
WIN7-10/ OSX 10.15.7
AC 5.1-25 USA