About 75% of .pdf files in web the read outloud option turned off, I am DISABLED can't see well, So,

This is not a setting that a file can set or disable. The application will allow you to do it if the file is readable. If the file consists only of images then there's no real text, and nothing can be read out loud. There's a function to convert image text to real text (called OCR), but not in the free version of Reader. You will need the paid-for Acrobat for that.

Hi there

Hope you are doing well and sorry for the trouble.

Accessibility features in Acrobat, Acrobat Reader, and Adobe Portable Document Format (PDF) enable people with disabilities to use PDF documents, with or without screen readers, screen magnifiers, and braille printers.

Acrobat supports assistive software and devices, such as screen readers and screen magnifiers, that enable visually impaired users to interact with computer applications. 

Use the Accessibility Setup Assistant to set up Reader for either a screen magnifier or a screen reader. Use the Accessibility Setup Assistant to improve how Acrobat interacts with the types of assistive software and devices that you use. Choose Edit > Accessibility > Setup Assistant, and then select the options you want from each screen of the Setup Assistant.

Read Out Loud is a Text-to-Speech (TTS) tool that is built into Adobe Reader. It reads text contained within a document window.

To use Read Out Loud, you need Adobe Reader and a Text-to-Speech engine installed on your system. Also the document must be accessible, otherwise it may not be read at all or it may be read in the wrong order.

For more information, please check the help page Accessibility features, Adobe Reader

Hope this information will help

Regards

Amal