1) It appears your layout AS BUILT is not correctly set to use a 24x36 paper size here, is it supposed to be, or is something odd at my end with your file?

2) Assuming your layout tab AS BUILT is the one you created (why is it rotated by the way?), and assuming the PLOT parameters I pulled up are the ones you saved and used in that layout, you have the plot scale set to FIT TO PAPER instead of 1:1, so there is your first mistake.

3) Then assuming, since you may or may not have missed "FIT" for a print scale in AutoCAD, you also may have missed FIT for a print scale in your PDF viewer as well instead of using ACTUAL SIZE or SCALE:100% to get everything correctly out of your PDF.