This is actually an Adobe issue, a recent update has caused the DBX and ARX applications to no longer work in AutoCAD.
Navigate to the directory shown in the Error (in the image above the path is C:\Program Files (x86)\Adobe\Acrobat DC\PDFMAKER\AutoCAD\2018\64)
Locate and rename the AcrobatAcadlc.dbx, AcrobatAcadlc.arx and PDFMAcad.arx and rename them to .old or some other extension (so AutoCAD cannot read them)
That will cause the error to no longer come up. You will still be able to Plot or Publish to PDF, but until Adobe fixes the issue, you will not have the Adobe Ribbon in your AutoCAD.
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