Although blur option is not inbuilt or avail there in Microsoft paint application,there is still possibilities you can make your project image or some confidential text blur, here i will show you in very simple step to do so.
Open the text or image you want to blur in paint application
Now select the portion from tools you want to make blur, then move the selected portion to some other area.
Re-size the selected area which you placed in other area, then make it smaller than the original size by holding one edge of the portion and drag it inward.
Now move the resized image to the original image area from where you had selected and moved then resize it again till it fit to the area.
I this post will be helpful for you let me know if you need same kind of topics so that i will guide you.