Hello Mohammad, how are you doing?
Welcome to the Microsoft community!
I'm glad to be able to assist you at this time.
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I'm sorry to hear that it's not working for PDFs on your mobile device.
One possible reason for this could be that the PDF you are trying to use the Read Aloud feature on is not compatible with Edge's PDF reader. In this case, you could try opening the PDF in a different PDF reader app and see if the Read Aloud feature works there.
If that doesn't work, you could try clearing the cache and cookies on your Edge browser or try reinstalling the app. These steps may help to resolve any issues with the Read Aloud feature.