To convert Convert PDF to Image and from Image to PDF, follow the below steps,*Install ImageMagick - https://help.ubuntu.com/community/ImageMagick

*For PDF to Image, from linux shell, type command

convert abc.pdf abc.jpg

*For Image to PDF, from linux shell, type command

convert *.jpg abc.pdf

Note- To get a higher quality image while converting from PDF to image, use options, like for example below

convert -quality 100 -density 600x600 multipage.pdf single%d.jpg

More about the options are available here - http://manpages.ubuntu.com/manpages/lucid/man1/convert.1.html