Here are some thoughts to help you decide what to do.
Cpu is not the only factor for a system's speed for office use. Hard disk plays a significant role (spinner or SSD) amount of ram, and software used. I will assume tho you can't do much about CPU and ram so if your hard disk is a spinner, consider swapping for an SSD, it will boost your everyday use by a LOT.
I mentioned software because people often overlook one factor. Newer software asks often for more recent hardware or has higher demands, especially in RAM. Since you didn't give us more info other than your CPU, I would suggest switching to older versions. Use windows LTSB or even windows 7 and office 2012 as an example. I often dont see people use the extra or new functions that newer software has, they just want the latest versions. Note here since you are an office user, and if you use things like printers, scanners, etc, avoid the light version of 10 as those have components missing that might give you problems in your everyday work, tho a test will tell you more.
If you can't do anything from the above, then as Charlie said above, a new PC is the only way.