How to split pdf file in windows?

It can be done using Google Chrome

    1)Drag and drop pdf file to chrome
    2)Click print from the toolbar which appears when mouse pointer placed on 
    bottom right corner or top right corner (Or Ctrl + P). 
    3)Select the pages you need to extract
    4)Click change button and select save as pdf instead of printer

I've had pretty good luck with PDF Split and Merge for doing this. Annoyingly, the current version attempts to install another product as well, so you'd want to deselect it when installing, so you'll want to beware of that. That annoyance aside, it works pretty well.

I've split a 46 page document at page 10 and 15 here - in your case you want to set it at 19 and 50. You just need to add the pages you want to split at seperated by a space.