Download Limit on PDF Download Button

I need a javascript/jquery code written for a Download button where they download a PDF. The button bust have a download limit I need to be able to change that to 30 or 300 or 3,000 or whatever other number I choose. It needs to be easily changed. It will just be a button with a link to a PDF that counts the amount of downloads it has, once it reaches that number it pops up a message that says. "All Downloads have Expired."