Welcome to Autodesk Forums!

Hi @Anonymous 

in order to be able to use .CTB file in the drawing, this drawing should be created from .CTB based template.

In AutoCAD for Mac there are four such templates:

acad -Named Plot Styles.dwt

acadISO -Named Plot Styles.dwt

acad -Named Plot Styles3D.dwt

acadISO -Named Plot Styles3D.dwt

If you already have drawing, you cannot convert it from STB based to CTB based in AutoCAD for Mac as you can do in AutoCAD for Windows. So the only one way is to create new drawing with one of CTB based template, select all in your existing drawing, copy to clipboard and paste to newly created file.