Questions and postings pertaining to the usage of ImageMagick regardless of the interface. This includes the command-line utilities, as well as the C and C++ APIs. Usage questions are like "How do I use ImageMagick to create drop shadows?".
WMF is a vector graphic and BMP is a (miserable) pixel grafic format. As with all vector formats, you should better use -density instead of -resize. Note that the density must be set before you load the vector image:
convert -density 100x100 test.wmf test.bmp
Via density, you may also adjust the aspect ratio. (Which what you possibly mean by "flattened".)
Anyway, as both, WMF and BMP, a proprietary Windows formats, you should probably better use a Windows program for this job. Give IrfanView a try, which also allows batch prcoessing and will produce better results in this special context.