A long search has ended... John's method works so my process to add text to the STEP models provided by the Integrated Circuit vendor supplied parts:
which leads to https://goo.gl/ZFhvHT
select Step and download it. drag RGY20_3P05x2P05.step out of the zip and open with TC. or use the attached steps.zip
(My first try)
Open the STP/STEP model, Alt+PgDw view Isometric SE, Text properties Text Color White Height 0.5 mm Mode Standard and enter the text needed. Select Simple Extrude then click on the text, tab to inspector bar, enter 0.001 for the height. Select the new Simple Excluded text, right click and select WorkPlane by Facet and select the top of the IC then drag the simple extrude to where it is needed. Select the text (not the extruded text) and delete it. I checked the simple extrude to make sure it was a solid and it was then saved the drawing.
But: TurboCAD changes the body of the device to gray, the same color as the pads. I've done this three times with different results each time.
On the original STEP model when I first imported/opened it and looked at it's properties the pen color was light gray for the body and leads, when I exploded the model everything was still light gray with TurboCAD but if you take the model and open it in FreeCAD the pads are light gray and the body is black. Same thing with my PCB software, gray/black.
Original model opened in TurboCAD
Original model opened in FreeCAD
Original model opened in DipTrace
Modified Original model opened in DipTrace after I changed the pads, body and added text, something I have not been able to repeat....
Why does TurboCAD change the model properties of a step image on open? After you open and try to exit without doing anything TurboCAD notifies you that the model has changed...