Add TextAnnotations (the ones from the top entry of the annotation toolbar) to PDF documents with various page sizes (e.g. A3, A4, letter, ...).
Select the icon by left-click. The size of the drawn rectangle shall match with the rendered icon.
Move the icon around by left-click + dragging. The size of the drawn rectangle shall match with the rendered icon.
Start Okular with different hidpi setting, e.g.
```
$ QT_SCREEN_SCALE_FACTORS='DVI-I-1=2;' okular
```
Repeat steps from above.