[magick-users] Problem converting to gray scale: PDF mangled

[Alastair Gregory]

Hi,
I'm using ImageMagick 6.2.5 on Linux and running

convert -colorspace GRAY infile.pdf outfile.pdf

where my input PDF is fairly large (~4.5MB) and is poster size: 46" x 
72".  I'm trying to convert the input PDF to a grayscale PDF.

The problem is, though the output PDF has the same dimensions, it looks 
like it is the result of "zooming in" on a portion of the input.

Can anyone suggest what I'm doing wrong?

Thanks!