When Reading Mode is enabled, you can't copy text from a pdf as well as add annotation to the pdf. This behavior is by design.
You may switch to Single Page/ Continuous to copy text from a pdf.
Let us know if you have any questions on this.
Thanks for your answer! When I'm reading book in foreign language, I want to use Google "tap to translate" feature. But I can't use it in Reading mode. Is there some other way to translate text in reading mode?
I have the same complaint. It does not allow to copy the text in Reading mode, forcing us to change the mode to copy and use the Google translator for example. Does Adobe have any intentions to include this simple and useful feature in its roadmap?
We are sorry for the inconvenience but currently, copying text in Reading mode is not available however you may file a feature request here: Feature Request/Bug Report Form