Hi Robert,
The images are so large it is a bit difficult to compare them but I could not see any difference between the two images - is there supposed to be a difference?
Using Acrobat is a different way to do vertical measurements and seems to work fine.
I presume you know that when you export the 2D DXF you can import it back into TFP again and do the measurements there? You need to set the DXF so it is 'unselectable', otherwise you keep accidentally selecting it, but then you can add anything, lines, circles, text, and any dimensions you want, just as you would on the plan. The dimensions still measure automatically. It can then be printed or sent to a PDF. If you are using it just to take some vertical measurement then just insert it on another location to do the measurements.
Allan