I have had a few requests for some type of page Highlighter. There are lots of these out there. Most of them (almost all) are Extensions or Add-ons to Browsers. This means if you want the highlighter to work you will need to be in a certain browser. That being said the one I recommend is Simple Highlighter. It is really easy, gives you colors to choose from and you can add notes/comments. It works great in Chrome.
Probably one of the BEST is Diigo. They were one of the first and only highlighter companies. Works really good. There is an Add On and Extension for Chrome and Firefox. It works really good. You do have to sign on with an account but it is worth it.
PROBLEMS – None of these work on a PDF.
For PDFs – I suggest you use Adobe Reader. You should have Adobe Reader on your computer. Otherwise it is a free download. It has some really good tools that people often over look. Many of use open our pdf’s on a Mac in Preview. Preview is OK but Adobe Reader does a much nicer job. Here is a Tutorial for using the Highlighter function in Adobe Reader.