PDF Expert 7 for iPad supports the Text to Speech feature to read the text in PDF files aloud.
How to read PDF text out loud:
Use the player controls to start reading the current page aloud or move to the next or previous page.
To start reading from a particular word or phrase, select it and tap Read from here in a pop-up menu.
To select another chapter in the document, tap .
Note: The Text to Speech feature is currently available only for iPad.
Here is the workaround for reading PDF text out loud on iPhone: