>What is the use of a "percentage difference" in the first place? Usually you want to know whether the files are identical or not; if they are not, you will have to do lots of manual comparisons (a tool that shows differences can help here), to see which version you will keep (or parts of both versions).

Here's the situation:

I have a customer who has a website that has about 15 pages that are similar. Each page has different content but much of the page is the same. She wants to be sure each page has enough distinct content so that no two pages are any more than 20% alike. We do not need to know what is different just how much they are different or alike.

Although I suppose if I could get a list of the differences and compare the size of the differences to the size of the files, that would also give me the percentages.