WordTalk

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From the authors:

For people with reading and writing difficulties, having text reinforced by hearing it read aloud can be very useful. Specialised programs have existed to do this for a long time, and in many cases are extremely helpful and highly appropriate and should be seriously considered, perhaps in consultation with professional advice where necessary. WordTalk is a free plug-in developed for use with all versions of Microsoft Word (from Word 97 upwards), which can help people with reading difficulties use Microsoft Word more effectively. It will speak the text of the document and will highlight it as it goes. It contains a talking dictionary to help decide which word spelling is most appropriate. It sits neatly in your toolbar and is highly configurable, allowing you to adjust the highlight colours, the voice and the speed of the speech.