Reader Question

David Parry bio photo By David Parry

A reader is looking for a software application to help her read digital documents, any suggestions on something which can do the following:

A rather mundane question I have for you. . . have you encountered something that could help make the reading process easier for digital documents? Something akin to dragging a colored index card along a page quickly as you read? I am a very fast reader with paper, but find my eyes wandering when looking at a screen. . . . My admittedly uninspired work-around is creating a word document, restoring down the screen, and using the little blue header to pull down on top of the digital document as I read. . . but a better solution would be just a colored floating bar that you could pull from your desktop and use as you are reading.

Anyone know of something that would work? Mac and/or PC?