Is 16GB worth it for that PC?

Yes. If you regularly have dozens of browser tabs open alongside Word, Excel, and a PDF reader, 8GB is probably your bottleneck. Doubling to 16GB gives you headroom so the system doesn’t have to swap memory to your hard drive constantly. The upgrade is cheap — used DDR3 sticks are a few bucks on eBay — and it’s probably the best performance-per-dollar upgrade you can do on that machine.