If you need to convert pdf to jpg I was working with php but it might be slow, obviously. But if you are using linux shell then it’s easier and faster.

72 dpi (web) = 595 X 842 pixels 
300 dpi (print) = 2480 X 3508 pixels 
600 dpi (print) = 4960 X 7016 pixels

https://stackoverflow.com/questions/43085889/how-to-convert-a-pdf-into-jpg-with-command-line-in-linux