The Imagemagick security policy seems to be not allowing me perform this conversion from pdf to png. Converting other extensions seem to be working, just not from pdf. I haven't changed any of the imagemagick settings since I installed it... I am using Arch Linux, if the OS matters.
user@machine $ convert -density 300 -depth 8 -quality 90 input.pdf output.pngconvert: attempt to perform an operation not allowed by the security policy `PDF' @ error/constitute.c/IsCoderAuthorized/408.convert: no images defined `output.png' @ error/convert.c/ConvertImageCommand/3288.