I have a new tip about batch converting cad files to any image type. Popular image viewer IrfanView now supports dxf format for free (new freeware dxf plugin in irfanview 4.35). I use irfanview for a long time cause it has great batch-process features. You can convert hundreds of your cad drawing files to pdf,bmp,jpg,png,gif or any other image format (irfanview supports over 100 different image file formats).