With AutoCAD, the units used are down to you.

Click here if you use 1 unit to represent 1mm

Printing a DWG To PDF.pc3 without layout

Scale 1:1 set 1000mm = 1 unit

Scale 1:50 set 20mm = 1 unit

Scale 1:100 set 10mm = 1 unit

Scale 1:200 set 5mm = 1 unit

Scale 1:500 set 2mm = 1 unit

Scale 1:1000 set 1mm = 1 unit

Click on one of the other options to activate the scale change before previewing.