If you want to print a QR code or a bar code on your structure, you can mark out their size (width & height) and the position and then inspect how they will fit the entire structure.
QR and bar codes areas are placed as text and can then be modified to the needed size and position. Then in the drawing's 3D view, you can view what the final structure looks like.
IMPORTANT: The QR and bar code areas that you mark out on your structure serve visualization purposes only, they do not apply the codes to the structure.