You can flip several annotations: polyline, polygon, pen, measure, angle and arrow.


Flip annotations with the "2D Actions" button:

1. Select the annotation object by clicking on it with the left mouse button. When an annotation object is selected, some green circles are displayed around its points.
2. Click on the "2D Actions" button of the 2D Viewer window. A menu will appear under your mouse cursor.
3. Click on "Flip Horizontally" or "Flip Vertically".

Example with a polygon object:

You can also flip annotations by 2 others methods: by the top menu of the 2D viewer window, or by the context menu.
See "How to launch actions".