I don't suppose you can. UNLESS: You know what standard they wrote the CTB to. By which I mean, what thickness centerlines, object lines, hidden lines etc should be. Then you could see what color each type of line is, and make a CTB to suit. Depending on what 'industry' these drawings are for, it could get really hairy. Especially if it's civil/site work.
There's a crap load of line types and thicknesses in some dirtworker drawings I've seen. Otherwise you'll just have to wing it and see how respectable you can make the drawing look with what you got. RE: missing ctb (Structural) 26 Nov 15 15:26.