Windows and Android apps for downloading and reading textbooks

I am in need of reader applications that are specifically optimized for textbooks. I would really appreciate if the application allows to search for and download textbooks directly without being restricted to content within a specific region/country, bookmark pages and have a simple and clean UI, apart from which I do not have any special requirements. I would ideally be looking for an application that can be installed both in my PC and mobile and allow syncing, however it is optional.