How do I use Mac's Preview application text speech feature?

There is a convenient way of making your Mac speak any selected text.

1. Open System Preferences.
2. Select Speech.
3. Select the Text to Speech tab if it is not already selected.
4. Check the box for Speak selected text when the key is pressed and provide a key combination of your choice.

You can now use the key combination to speak selected text system-wide.

I read the above comment and tried to follow the instructions I was unsuccessful (as I didn't highlight the text). Although, having now solved the issue you need to highlight the selected text and then press the key combination (mine is ctrl+s).

Now I use it on all applications including preview, Microsoft Word, chrome etc. I love it.