Adding new button on pdf viewer

[MarioZagreb]

Hello,

When I click on a document in my document library (in SP Online), it opens in a viewer in browser.
Is it possible to add a new button on that viewer?

I noticed that this is a "spCommandBar".
I have managed to add a new button (by creating a SPfx extension) to a spCommandBar of a document library. How do I add the same button in spCommadBar of document viewer?

[MarioZagreb]

It isn't possible?

[PzKfWg]

Did you ever figure it out?