If your Document Info Record has several viewables attached you can define the order for the default viewing format, which is used in the embedded VE Viewer in SAP ECTR.
Change the following entries in your config file "<SAP ECTR Inst Directory>\\addons\sapvev\customize\config\default.txt":
# Send these wsappl originals to the embedded VE viewer
plm.2dpreview.drawings.wsappl = JTM;RHM;JT;RH
# Supported file extensions for the viewer (in this case JT is used first. If not available RH is used)
plm.viewer.ve.viewable.formats=jt;rh