I have installed an older free version of DraftSight after not being able to get the 2015 free version to run on my Windows Vista machine no matter what I did.  I believe this is the 2011 version.  It has work fine for new drawings, but I have come across a strange issue with drawings that I had drawn on a 2011 AutoCAD student version.  Some of the drawings I can open, no problem, it just seems to run a bit slow when updating or making changes.  But then on other drawings, DraftSight stops responding as soon as I try to open the drawing.  What could be causing this problem?  How do I solve it, so that I can open and use these drawings?  I also noticed that I can't export a pdf of a drawing.  Another issue I could use help solving.