Can't find the stamp option in Adobe Acrobat DC

I'm going round in circles trying to find the stamp option. I have the free version of Adobe Acrobat DC on a Chromebook and have tried it in the app (in which there hardly seem to be any tools, see attached screenshot) and also the browser version.

Acrobat support says there are stamps in the free version of Adobe Acrobat DC. One guide I found says to click 'All tools'. When I do that it brings up the paid option (which I have tried and still can't find stamps). I found another recent article saying that the stamps option should appear under the Comment button. It doesn't in my version.

I'm tearing my hair out. Can anyone help? I'd appreciate it if you could explain it to me like I'm five as I haven't used Acrobat for years.