As far as I see, there are two different problems involved, which have two different solutions:
1- Copyright issue. You build a file, you want to have the benefits. You do not want to see this files used by third parties, claiming they are theirs.
This problem is common with a LOT of digital material (maybe all material). Once it is replicable, anyone can claim ownership, and this matter can only be solved in court.
Luckily, unlike written text or music, a ArchiCAD (or any other BIM) file is not something easily appropriated. For one, each project is a projects, so there is no special interest in stealing another guys idea, just on reproducing certain aspects and detail of this idea, which is something architects have always done. On the other hand, the very complex structure of any given file of a medium to big size project makes it almost impossible to a third party to take advantage of it. It is easier to just copy it manually (having the plans printed and then building them from scratch, with your own layer/pens/plotmaker/everything settings). This of course is also possible from a pdf or a paper document, so there is no specific problem here.
2- Contractor changing your drawings and then claiming these changes were not made by him. This is a very serious problem, because if you are not careful beforehand, you can get into a whole lot of trouble (even legal trouble).
The american way of solving it (afayk) is putting a disclaimer on each file and drawing. This way, if the going ever gets tough, you can easily bail out. I am not particularly fond of this method.
There are other methods you can try to implement, my favorite (because of its simplicity) being:
You make two DVDs (locked) of the files. You sign both of them (physically sign the DVD, like any paper document), your client signs both, and each one of you keeps one copy.
Obviously, if suddenly a document used by the contractor is different from your own, you just have to fetch both DVDs and verify which one is true. You can even have a third DVD kept by a third party, as a backup.
Obviously also, as soon as your contractor knows there is a DVD out there with the original files physically signed by him, he will think twice before making any (even accidental) change.
This method seems very reasonable to me, and the contractor can not complain you are being paranoid. After all, this is exactly what allays has been done every time you handed a drawing over. You signed, the contractor signed it, and this made the drawing official.
Hope this helped.
MK
