Solid Works, a drawing software company, has attempted to do for 3-D drawings what Adobe and the .pdf format did for document sharing. They've created a free viewer and dramatically smaller file that can be e-mailed, shared and preserved, but cannot be edited, by the recipient. For those who actually need to do something with the files rather than just look at them, this causes a problem. Converting between .edrw (Solid Works' file extension) and a usable document like a .dwg for AutoCAD isn't easy, and it's best handled by the sender rather than the recipient, but there is an acceptable workaround.
Contact the sender of the .edrw file to see if he has the paid version of Solid Works (the program that created the file). The paid version allows a conversion to AutoCAD file type .dxf. When you receive the .dxf, you can import that file into AutoCAD and "Save As" a .dwg. There is a definite possibility of fidelity loss with this method.
Download the Solid Works eDrawing viewer for free. It is available at the Solid Works website linked in the Resources below.
Download and install the DWG Export for Solid Works tool. The cost for a license as of 2009 is 195 Euro. Currency fluctuations and your bank's fees for foreign currency transactions will affect the actual price if you are outside the European Union.
Use the DWG Export plug in for Solid Works to convert your file to .dwg. The program adds new menu items to the Solid Works file menu including "Export to .dwg."