Stop whatever you are doing. You run the risk of "infecting" all of your company's drawings.
First. Click on the link below to obtain a copy (at a small price) of a piece of software that will identify all the infected drawings.
You're looking for a product called EDU-Scan.
"EDU-Scan is designed to prevent commercial drawings from accidentally becoming contaminated with a plot stamp that accompanies any drawing content originating from an Autodesk Educational Market Release product."
Second. Contact your authorized AutoCAD dealer. Tell them the problem and ask for their help. You'll have to prove you are a legit user but it should be pretty straightforward if you have dealt with the same dealer in the past. Then request a copy of EMR_utility. It comes with a 15 day time limit. It will remove the educational stamp from your drawings. The software should not be passed on to others with the same problem as AutoDesk is adamant about this point.
Third. Fire the employee who did this to you. He should have known what would happen if the drawing or any part of it was used for commercial purposes.
Finally, set up a procedure to use drawing viewer software to print a copy of any new drawing being introduced into your system. The educational stamp should show up in the plot.
By the way, don't try blaming AutoDesk. They assume no responsibility for the illegal use of their educational software and the drawings produced by same when used in a commercial business. User beware. Note: ACAD 2004 and later releases supposedly warn the CAD operator that they are about to open a drawing done with educational versions of AutoCAD.