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Your question is a good one. Independent of a having a specific contact at an potential employer, it is best to identify the individual responsible for hiring. More specifically, if you are looking for a CAD position ... call the prospective employer and ask to speak to the CAD supervisor, manager, etc. Your goal is to determine whom, at the company, you should direct your resume and cover letter. Try to avoid the Human Resources Department.
Use Free-Resume-Builder.net's (http://www.free-resume-builder.net) free online resume and career letter builder tool to build your CAD resume and cover letter.
Good luck.