emacs zoom in/out globally

Question

I know that I can zoom in/out using C-x C-+, but this applies only to the current file. Once I open another one, the text goes back to the default value and it\'s really tiresom

Answer 1

connected to a beamer while giving a presentation.

There is another package for that!

emacs-presentation-mode

Quoting from the site

1. Execute M-x presentation-mode to start the presentation.
2. Adjust scale size by C-x C-+ or C-x C-- See https://www.gnu.org/software/emacs/manual/html_node/emacs/Text-Scale.html
3. After the presentation, execute M-x presentation-mode again.
4. And then execute M-x presentation-mode again, the last scale will be reproduced.
5. If you want to persistize its size as the default size of presentation-mode after restarting Emacs, set presentation-default-text-scale.

It's also have description of differences from other similar modes/package.