we imported a .pdf with a 3:1 scale.  when we try to scale it down to size, the measurements are all off by small amounts.  is there any way to scale down 1 specific 'edge' to a specific length and have the rest of the image scale with it?  Or if theres an easier way what is it??

If you know the exact scale, just type in "/3" or "*3" at the end of the dimensions on the toolbar (ie if the size reads "12mm" it should now read "12mm*3" or "12*3mm" or just "12*3" Hit return or click somewhere and the size will update.

Alternate method is to draw a line/box of X, then shrink it and use it for snapping the other stuff to. Usefull if you don't know the scale.

Also be aware that the printer may not print a true 1:1 Draw a box of a specific size and print it, then measure it. You may have to squish the image to get it to print properly (using the second method above)