Each page of a PDF your file has will be its own section of comments that can be tracked on Wipster. Multiple pages means multiple fields of commenting you can post. There will be a counter on the top-left showing you which page you are on and how many you have to view. Just switch through the page counter to view each individual page.
When you leave comments, you can also track which page it came from by opening up the to-do list and clicking on the respective thumbnail of the comment you want to read.