If a parallelogram has a right angle is it a rectangle?

No because it could be an irregular quadrilateral that includes a right angle. A rectangle has 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.

It is true that you can draw an irregular quadrilateral with a right angle which is not a rectangle but the figure will not be a parallelogram.