WMF is primarily used for vector line drawings. You may be able to use one of these other programs to do the file conversion and see if you get better results.
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I am using autocad map 2017, I am exporting one drawing that is about 5m.
Here is a great link, https://knowledge.autodesk.com/support/autocad/getting-started/caas/CloudHelp/cloudhelp/2016/ENU/AutoCAD-Core/files/GUID-DF7E2411-C49B-4E51-AF58-32EC2EE1C809-htm.html
However you can convert dwg to dxf or jpg also.