Using an Autodesk educational product marks each drawing file so that when you go to print, you see a "Produced by an Autodesk Educational Product" or "For Educational Use Only" watermark in the margins of the plot. This is a bad joke...even blood-sucking Microsoft doesn't put any restrictions on the free educational software they distribute.
If you're using AutoCAD and happen to have a normal (non-educational) copy handy, you can just export the drawing as a .dxf (using the DXFOUT command), import the .dxf (using the DXFIN command), and save it as a .dwg. Alternatively, you can create a new drawing, insert the educational drawing as an xref, bind it, and explode the resulting block. Both of these methods will remove the watermark forever. However, they only work if you have a non-educational version of AutoCAD and obviously won't work for Inventor.
Most effective and universal method:
Since this educational infection only affects plots...
1. Plot the drawing as a PDF file using either the built-in PDF driver or a third party PDF printer (I like PDFill).
2. Edit the PDF file using a free tool like PDF-XChange Viewer and put white rectangles over top of the watermarks, effectively erasing them (or just delete the text itself if you have access to software that can truly edit the PDF).
3. Plot the PDF file.
It's a hassle, but it's the only way when all you have handy is an educational version.