To convert pdf to image files use following commands:
For PNG gs -sDEVICE=png16m -dTextAlphaBits=4 -r300 -o a.png a.pdf
For JPG gs -sDEVICE=jpeg -dTextAlphaBits=4 -r300 -o a.jpg a.pdf
If you have multiple pages add to name %03d gs -o a%03d.jpg a.pdf
gs -sDEVICE=jpeg -dTextAlphaBits=4 -r300 -o a%03d.jpg a.pdf
What each option means:
sDEVICE={jpeg,pngalpha,png16m...} - filetype
-o - output file (%stdout to stdout)
-dTextAlphaBits=4 - font antialiasing.
-r300 - 300 dpi
Taken from https://stackoverflow.com/a/33528730/1700479
Credits: https://stackoverflow.com/users/4355809/yanpas and https://stackoverflow.com/users/390722/startupguy