Used AutoDWG DWGLock for Windows?
Developer’s Description
By AutoDWG
A dwg tools, protecting drawing file, Keep others from modifying/copying your design. DWGLock is a stand-alone application, no autoCAD required. Supports autoCAD R2.9 thru 2009 drawings. Powerful encryption, secure the entities in the drawing, they can not copy nor change it. Recipients can open up protected drawing, and add lines etc to the drawing file.
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