A CAD file for making printed circuit boards is like a photograph, with the line widths, pad and hole sizes all part of the file. There are two ways this happens. First, with a "captive" drafting program. It's a freebie download, but the CAD file that comes out of it is not standard, only works if you upload and buy from the outfit who provided the program. Expresspcb is set up this way.
Second method is a CAD program that lays out all those same details but saves them in an industry-standard set of files loosely referred to as "Gerber" format. A significant majority of pcb fabrication sources use this format.
Either way you end up drawing a picture of the board that will get made.
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