I'm quite confused by these two terms because different websites define them differently.
Profit margin is profit after the cost of sales. If you review an income statement, you will see revenue, and then typically a data field called “cost of selling goods”. Revenue - Cost of sales is profit margin.
Net profit margin is Revenue - all expenses. So this includes taxes, interest expense, administrative expenses, and ALL expenses. An easy way to remember this is that profit margin is simply revenue - the cost of selling products, and net profit margin is revenue - ALL costs.