Hello, I am using qcad pro. I’m pretty new to cad. i used an older version of auto cad about 20 some years ago. Don’t remember much. I’m just trying to figure out how to soften the corners on a rectangle. if there is a qcad for dummies book out there I would love to know how to find a copy. 
To round corners, you can use:
Modify > Round
Note that the rectangle tools also have a radius option:
Draw > Shape > Rectangle
→ see “shape options”
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Official QCAD video tutorials: