Improved MacOS "spoken content" functionality in Acrobat for Mac
The text reader in MacOS is not a typical screen reader, but it does provide easy, fast access to spoken content from on-screen text. Unfortunately, it does not work with Adobe Acrobat. Ideally, it would speak selected text with a keyboard shortcut, but only reads the document name in Adobe Acrobat. The Acrobat screen reader is difficult to use, does not read selected text, and often fails due to pdf accessibility issues.
I understand the issue faced by you. Read Out Loud is not a screen reader provided by Acrobat but a feature to read the pdf.
You can user VoiceOver on MacOS which is a Screen Reader supported by Apple. You can easily find the shortcuts at https://www.apple.com/voiceover/info/guide/_1131.html
I hope this would help you in resolving the issue.