In most cases, you cannot directly convert .edrw files (SolidWorks eDrawing) to anything else, simply because these files were exported in a publishing format that is only meant for viewing and not for further editing.
It largely depends whenever the file was 'locked' during the export. Unlocked files may be potentially opened in SolidWorks (with eDrawing plugin of sorts) and saved as standard files. For locked files, there is really no way to directly recover them unless you have access to the source.
In these cases, the best course of action is to obtain the original SolidWorks source (most likely .slddrw file), which can be potentially exported to DWG format in several programs or even dedicated CAD converters (see slddrw to dwg conversion).
However, it is likely that to handle these files, you will need access to SolidWorks and third party apps won't help you much.
Updated: November 3, 2016