Get a preview JPEG of a PDF on Windows?

ImageMagick delegates the PDF->bitmap conversion to GhostScript anyway, so here's a command you can use (it's based on the actual command listed by the ps:alpha delegate in ImageMagick, just adjusted to use JPEG as output):

gs -q -dQUIET -dPARANOIDSAFER -dBATCH -dNOPAUSE -dNOPROMPT \
-dMaxBitmap=500000000 -dLastPage=1 -dAlignToPixels=0 -dGridFitTT=0 \
-sDEVICE=jpeg -dTextAlphaBits=4 -dGraphicsAlphaBits=4 -r72x72 \
-sOutputFile=$OUTPUT -f$INPUT

where $OUTPUT and $INPUT are the output and input filenames. Adjust the 72x72 to whatever resolution you need. (Obviously, strip out the backslashes if you're writing out the whole command as one line.)

This is good for two reasons:

1. You don't need to have ImageMagick installed anymore. Not that I have anything against ImageMagick (I love it to bits), but I believe in simple solutions.
2. ImageMagick does a two-step conversion. First PDF->PPM, then PPM->JPEG. This way, the conversion is one-step.

Other things to consider: with the files I've tested, PNG compresses better than JPEG. If you want to use PNG, change the -sDEVICE=jpeg to -sDEVICE=png16m.

You can use ImageMagick's convert utility for this, see some examples in http://studio.imagemagick.org/pipermail/magick-users/2002-May/002636.html :

Convert taxes.pdf taxes.jpg 

Will convert a two page PDF file into [2] jpeg files: taxes.jpg.0, taxes.jpg.1

I can also convert these JPEGS to a thumbnail as follows:

convert -size 120x120 taxes.jpg.0 -geometry 120x120 +profile '*' thumbnail.jpg

I can even convert the PDF directly to a jpeg thumbnail as follows:

convert -size 120x120 taxes.pdf -geometry 120x120 +profile '*' thumbnail.jpg

This will result in a thumbnail.jpg.0 and thumbnail.jpg.1 for the two pages.