Reference Scale

I have taken a pdf generated from cad, In Inkscape I converted it to a DXF file.

I opened the dxf file in LibreCAD, however the countertops are 38.xxx" deep and is I use the scale command it already has a scale factor. Of what I don't know.

I need to be able to scale the entire drawing using two points of a line of my countertop and tell it that distance should be 24" and the rest of the drawing scales accordingly.

Assuming your default units already are in inches, otherwise change the drawing to the units you will be using before any measurement.

measure a line with known measures, If I understand correctly, you say countertop should be 24" but it currently measures 38"
select the entire drawing entities, then scale
select a base point anywhere it makes sense, it is not so important as you scale everything.
In the popup dialog set the scale to 24/measured_distance
done

HTH

A little late to the party.  As a Civil Engineer, I am used to scaling up/down as elements outside of the building envelope may require.  I measure an element in the drawing (say - a line, maybe a property line - or the width of a desk or interior wall if inside the building envelope), one that is long, and one that has a known dimension.  If the element measured is too long (say), I divide the smaller known dimension by the larger measured dimension to establish the percentage of scale reduction required.  Then I command:

SCALE==>(Select to scale)
SELECT ALL [button]==>
right click again in the drawing==>
SCALE==>(Select reference point)
0,0 [or other appropriate reference point]==>
[load the calculated percentage into the ISOTROPIC SCALE menu]==>
<ENTER>

Save Early - Save Often, in particular immediately prior to SCALE.  

Warning:  Some blocks do not react well to scaling; dimension arrowhead blocks from AutoCAD in particular.  

UNDO (after SCALE) doesn't get it done for me.  Is there a presetting for the amount of allowable buffer?

When a commands "blow up" unexpectedly (I am new to LibreCAD), I close and reload the drawing, then try something else.