If a parallelogram has a right angle then it is a rectangle?
No because it could be a right angled trapezoid.
A rectangle must have four right angles.
Yes, a parallelogram with a right angle is always a rectangle.
In fact, in my geometry book, some 55 years ago such was the
definition of rectangle.
A parallelogram with one right angle will always have four right
angles.
The right angled trapezoids that are not rectangles are not
parallelograms.