look at halftoning: type is too light, backgrounds much too dark
I prefer to read documentation in printed form in part because of limited space on my monitor. But not many docs these days are provided in anything but html. So your service is potentially a good way to get a printable copy without my first passing the web pages through page-makeup software and doing the required handwork.
But the current version of your software is specifying halftones to the printer in a funny way that makes text almost unreadably light and background tints unreadably dark. The converted file looks okay in the pdf reader, but when printed it's quite a mess, and unusable.
The problem is not in the reader or the printer, because I can get perfectly fine tinted text and backgrounds from the pdfs I export from InDesign3.