Adobe - Warning Empty Page - Read Out Loud

[ZedCar]

I have tried listening to books in PDF format using the Adobe 'Read Out Loud' function in their PDF reader.

It works without problem on one book, though on a second book the voice states "Warning! Empty page." for every page in the book.

Would anyone have any ideas as to what might be wrong?

Thank you.

 

[Borek]

Can you mark text in the other book? Sometimes books in pdf format are just scanned images, without OCR.

 

[ZedCar]

I can highlight the text in both books using the cursor.

So the book is not composed of scanned images.