When I open the DXF file in LibreCAD, then it shows the correct size of an object, but when I import that file in Blender, then the size of that object becomes very large.
Your DXF file is using 1 unit == 1 inch, so the marked length is $11\cdot 12 + 11.2780 = 143.278"$ long. Blender's internal unit is 1 meter long, so the DXF imports as 143.278 meters, and $ \frac{143.278}{0.3048} \approx 470'$ which is what's being displayed.
You could fix this by entering 0.0254 in the "Unit Scale Box." That will give you correct readings, but will still be insanely huge.
You could fix this by scaling the DXF by 0.0254 manually after you import it, or you could enter 0.0254 in the unit scale box of the DXF importer