First open the cad, then open the file. The specific method is (the following is plagiarism, but it is feasible, pay attention to the operation in the last paragraph):

Method 1: First save the file in dxf format, then reopen CAD, open the newly saved dxf file, save it in dwg format, and overwrite the original file, removing the production mark when printing Autodesk Education Edition.

Method 2: Save the drawing file in R 12 DXF format, then reopen CAD, open the newly saved file in R 12 DXF format, save it as dwg format, and overwrite the original file to remove the production mark when printing Autodesk Education Edition.

Do as above, save the file in DXF format or R 12/R 14 format, and then open it with CAD. There was something wrong when I opened it. Unable to open this DXF file, an error occurred. Press enter to continue. There was nothing. Facts have proved that this method is not effective for more complex files, and can only solve CAD drawings with little information.

Try clicking File-Drawing Utility-Check in the CAD menu bar again. Check the errors in the drawings first, find out the thickness of the errors, and then "correct". Then, according to the above method 1, get it! Problem solved. Using method 2, the problem can also be solved.