Sending autocad hull section files has become so effortless and common that I sometimes forget that not everybody knows what they are.  When I end up spending a lot of time explaining autocad files, it must mean it’s time for a blog post on them.  First, a *.dxf or *.dwg autocad file is a vector file. That is compared to a raster file such as a jpeg or even PDF.  In a vector file a line for example is defined as being a single entity lying between two points.  In a raster file a line is hundreds or thousands of dots.
That means a line in a vector file is of a definable physical size. Not so with a raster file. In CADD files, that size is almost always real world size. Not to any scale. Real world. What scale are you now? None, you are real world size. Same thing with a dxf file that I send to you. Scale only enters in when it is plotted out.
The one catch however is numeric base or format. Every CADD file has an underlying numeric basis. It could be inches or feet or meters or millimeters. When a dxf file is sent from one computer to another, odds are the numeric base will not be the same. The file you get might be 39.64 times too large or small. Or maybe just 3.something different.  It will be one of  those ratios between imperial and metric usually.  That is why I try to include a scale divot in every file. Its typically on the lower right near the page number. Do a measure distance on it and see if it matches what it should. If not you can easily rescale the drawing to match your own machines real world. Once you have done that, you can do a measure distance on anything and get its size.