The Mac system is very intuitive but one thing that is different from Windows systems is that it allows us to interact with the files in the Preview application just by selecting them and pressing the space bar.
However, if we have, for example, a file in PDF format in which we want to make a text capture of it without having to open it, it is not possible natively. In the Quick View Preview you can allows you to see all the pages that compose it but does not allow you to select anything of it to copy.
La Preview is a wonderful macOS utility that allows you to preview your files just by pressing the space bar. If you want to allow that you can also copy text from quick view,you can do the following:
defaults write com.apple.finder QLEnableTextSelection -bool TRUE; killall finder
As you can see, in a very simple way and with a Terminal command that, if you analyze it, is perfectly understood, we can make the Preview application much richer thanks to this improvement in the quick view of files.
If the change you have made does not convince you at all, you can always revert the command with this other command that simply tells the system the opposite:
defaults write com.apple.finder QLEnableTextSelection -bool FALSE; killall Finder
Once the command is executed, the Finder will restart and from that moment you will be able to preview a text document or a PDF and be able to select part of the text to copy or select it and click to drag it over another document.