Here are several screen reader options.
Most Operating Systems have built-in screen reading capability. Often, that works best because it works with nearly everything.
Also, the Books Apps on iOS (iPad) or Kindle on Amazon Tablets have built in screen reading. You can import PDFs into both of those apps. There are many videos on YouTube on how to do this.
ACHS has found Natural Reader to be one of the best, it works well with our online courses. There is a paid and a free version. Speechify is another that people say works great, but it has a $70 yearly fee.
For more information, see this helpful PDF.