If you try to access the PDF document with Google Quality Raters Guidelines, you will have bad luck. The PDF appears to have been removed from Google's servers. This happened before and when that happened it was a mistake, Google solved it. This time I suspect that it is almost a mistake and Google will fix it.
If you try to access the PDF by going directly to it or just googling it and clicking on the result [guidelines for Google Quality Raters], it is currently 404 for you.
Again, I assume it will come back soon, but if not, you can get an archived version here or on the Wayback machine.
Forum discussion on twitter.
Update: there is a URL on the Google server that works, on the ratershub here.