This is not the most efficient, and I'm sure that there has to be a better way.  Does anyone have any suggestions for any freeware (or very low cost) or workflow standards to make this task easier?  

Thanks.

Rick

With respect to the "original drawings", I should have been more clear.  The original drawings are usually hardcopies which I scan into PDF format.  Most of the proprietors are small businesses who can't afford an engineering department and wouldn't know what a DWG-formatted drawing is.   My issue is that over the years, the proprietors of the facilities are not-so-diligent about keeping drawings updated.  Work is done by multiple vendors and although the proprietor is responsible for his Management of Change (MOC) process he lacks the tools and knowledge to capture the changes on a drawing.  My wishful thinking is that I can find a tool that is inexpensive and simple enough that the vendor, the proprietor, or both can capture the changes.   The captured changes might be as simple as erasing the portions which have been physically removed and providing a Note "triangle" and a reference to a block of text describing the change.  In my role, I help bridge the gap between the proprietor and the vendor doing the physical work.  I like to provide an accurate record of what has been done, clean  up the other changes not previously recorded, and establish a standard for how future changes should be captured.  

Sounds like I may need to take a few CAD courses and invest some time in a tool to manipulate DWG-formatted drawings to capture what I want to capture.  Next question:  Is there an inexpensive tool that can take a PDF and convert it to a DWG?    And next... a reasonably inexpensive tool for altering the DWGs?  Autocad appears to be the standard, but is there something a bit more bare-bones?   Any good comparisons you can point me to?  Excuse the uninformed questions, but I am pretty low on the learning curve.  I used to be with a rather large engineering firm and I usually just had to hand off marked up hardcopies to our draftsman/CAD operator who would work his magic.

Thanks again.

Rick